public class FirstTest {

    public int add(int a, int b) {
        return a + b;
    }

    @Test
    public void testAdd(){
        FirstTest firstTest = new FirstTest();
        int result = firstTest.add(1,2);
        //  assertEquals(4,result); 
        assertEquals(3,result);
    }

    <!--
       - 如果判断不相等的时候，后台报错信息
       - java.lang.AssertionError: 
       - Expected :4
       - Actual   :3
       - <Click to see difference>
     -->

}

public class AssertTests {
  @Test
  public void testAssertArrayEquals() {
    byte[] expected = "trial".getBytes();
    byte[] actual = "trial".getBytes();
    assertArrayEquals("failure - byte arrays not same", expected, actual);
  }

  @Test
  public void testAssertEquals() {
    assertEquals("failure - strings are not equal", "text", "text");
  }

  @Test
  public void testAssertFalse() {
    assertFalse("failure - should be false", false);
  }

  @Test
  public void testAssertNotNull() {
    assertNotNull("should not be null", new Object());
  }

  @Test
  public void testAssertNotSame() {
    assertNotSame("should not be same Object", new Object(), new Object());
  }

  @Test
  public void testAssertNull() {
    assertNull("should be null", null);
  }

  @Test
  public void testAssertSame() {
    Integer aNumber = Integer.valueOf(768);
    assertSame("should be same", aNumber, aNumber);
  }

  // JUnit Matchers assertThat
  @Test
  public void testAssertThatBothContainsString() {
    assertThat("albumen", both(containsString("a")).and(containsString("b")));
  }

  @Test
  public void testAssertThatHasItems() {
    assertThat(Arrays.asList("one", "two", "three"), hasItems("one", "three"));
  }

  @Test
  public void testAssertThatEveryItemContainsString() {
    assertThat(Arrays.asList(new String[] { "fun", "ban", "net" }), everyItem(containsString("n")));
  }

  // Core Hamcrest Matchers with assertThat
  @Test
  public void testAssertThatHamcrestCoreMatchers() {
    assertThat("good", allOf(equalTo("good"), startsWith("good")));
    assertThat("good", not(allOf(equalTo("bad"), equalTo("good"))));
    assertThat("good", anyOf(equalTo("bad"), equalTo("good")));
    assertThat(7, not(CombinableMatcher.<Integer> either(equalTo(3)).or(equalTo(4))));
    assertThat(new Object(), not(sameInstance(new Object())));
  }

  @Test
  public void testAssertTrue() {
    assertTrue("failure - should be true", true);
  }
}

@Test(expected = IndexOutOfBoundsException.class)
public void testException(){
    new ArrayList<Integer>().get(0);
}

@Test
public void testTryCatch(){
    try {
        new ArrayList<Integer>().get(0);
        fail("失败信息");
    }catch (IndexOutOfBoundsException indexOutOfBoundsExecption){
          assertThat(indexOutOfBoundsExecption.getMessage(), is("Index: 0, Size: 0"));
    }
}

@Rule
public ExpectedException thrown = ExpectedException.none();

@Test
public void testExpectException(){
    List<Object> list = new ArrayList<Object>();
    thrown.expect(IndexOutOfBoundsException.class);
    thrown.expectMessage("Index: 0, Size: 0");
    list.get(0); // execution will never get past this line
}

assertThat(x, is(3));
assertThat(x, is(not(4)));
assertThat(responseString, either(containsString("color")).or(containsString("colour")));
assertThat(myList, hasItem("3"));

/**
 * Some simple tests.
 */
public class SimpleTest extends TestCase {
    protected int fValue1;
    protected int fValue2;

    @Override
    protected void setUp() {
        fValue1 = 2;
        fValue2 = 3;
    }

    public static Test suite() {

        /*
           * the type safe way
           *
          TestSuite suite= new TestSuite();
          suite.addTest(
              new SimpleTest("add") {
                   protected void runTest() { testAdd(); }
              }
          );

          suite.addTest(
              new SimpleTest("testDivideByZero") {
                   protected void runTest() { testDivideByZero(); }
              }
          );
          return suite;
          */

        /*
         * the dynamic way
         */
        return new TestSuite(SimpleTest.class);
    }

    public void testAdd() {
        double result = fValue1 + fValue2;
        // forced failure result == 5
        assertTrue(result == 6);
    }

    public int unused;

    public void testDivideByZero() {
        int zero = 0;
        int result = 8 / zero;
        unused = result; // avoid warning for not using result
    }

    public void testEquals() {
        assertEquals(12, 12);
        assertEquals(12L, 12L);
        assertEquals(new Long(12), new Long(12));

        assertEquals("Size", 12, 13);
        assertEquals("Capacity", 12.0, 11.99, 0.0);
    }

    public static void main(String[] args) {
        junit.textui.TestRunner.run(suite());
    }
}

public TestSuite(final Class<?> theClass) {
        addTestsFromTestCase(theClass);
    }
private void addTestsFromTestCase(final Class<?> theClass) {
        fName = theClass.getName();
        try {
            getTestConstructor(theClass); // Avoid generating multiple error messages
        } catch (NoSuchMethodException e) {
            addTest(warning("Class " + theClass.getName() + " has no public constructor TestCase(String name) or TestCase()"));
            return;

        }
// 这个类是否是public的 如果不是 发出warning ，并且fail(message)
        if (!Modifier.isPublic(theClass.getModifiers())) {
            addTest(warning("Class " + theClass.getName() + " is not public"));
            return;
        }

        Class<?> superClass = theClass;
        List<String> names = new ArrayList<String>();
//        这句话说明的是如果这个类是superClass的超类，或者接口就返回true，否则返回false
        while (Test.class.isAssignableFrom(superClass)) {
//            如果是true  有顺序的返回声明的方法
            for (Method each : MethodSorter.getDeclaredMethods(superClass)) {
                addTestMethod(each, names, theClass);
            }
//            获得superclass类，递归的查找test方法
            superClass = superClass.getSuperclass();
        }
        if (fTests.size() == 0) {
            addTest(warning("No tests found in " + theClass.getName()));
        }
    }

private void addTestMethod(Method m, List<String> names, Class<?> theClass) {
// 获得方法名如果list数组中已经包含这个方法名，就直接退出
        String name = m.getName();
        if (names.contains(name)) {
            return;
        }
        if (!isPublicTestMethod(m)) {
            if (isTestMethod(m)) {
                addTest(warning("Test method isn't public: " + m.getName() + "(" + theClass.getCanonicalName() + ")"));
            }
            return;
        }
// 把这个方法名加入到names List中
        names.add(name);
        addTest(createTest(theClass, name));
    }
//再来看外层的addTest方法 把拥有的test方法放到fTests中。
public void addTest(Test test) {
        fTests.add(test);
    }

static public Test createTest(Class<?> theClass, String name) {
        Constructor<?> constructor;
        try {
            constructor = getTestConstructor(theClass);
        } catch (NoSuchMethodException e) {
            return warning("Class " + theClass.getName() + " has no public constructor TestCase(String name) or TestCase()");
        }
        Object test;
	// 通过反射方式获得方法的test实例
        try {
            if (constructor.getParameterTypes().length == 0) {
                test = constructor.newInstance(new Object[0]);
                if (test instanceof TestCase) {
                    ((TestCase) test).setName(name);//如果继承TestCase
                }
            } else {
                test = constructor.newInstance(new Object[]{name});
            }
        } catch (InstantiationException e) {
            return (warning("Cannot instantiate test case: " + name + " (" + Throwables.getStacktrace(e) + ")"));
        } catch (InvocationTargetException e) {
            return (warning("Exception in constructor: " + name + " (" + Throwables.getStacktrace(e.getTargetException()) + ")"));
        } catch (IllegalAccessException e) {
            return (warning("Cannot access test case: " + name + " (" + Throwables.getStacktrace(e) + ")"));
        }
        return (Test) test;
    }

public static void main(String[] args) {
        junit.textui.TestRunner.run(suite());
    }
// 使用TestRunner的run的静态方法 返回一个TestResult用来返回结果。   
static public TestResult run(Test test) {
        TestRunner runner = new TestRunner();
        return runner.doRun(test);
    }
// 调用runner的doRun方法
public TestResult doRun(Test test) {
        return doRun(test, false);
    }
public TestResult doRun(Test suite, boolean wait) {
//      用来返回结果的TestResult
        TestResult result = createTestResult();
	// 注册一个TestListener
        result.addListener(fPrinter);
        long startTime = System.currentTimeMillis();
//      test.run方法
        suite.run(result);
        long endTime = System.currentTimeMillis();
        long runTime = endTime - startTime;
        fPrinter.print(result, runTime);
        pause(wait);
        return result;
    }

/**
 * Creates the TestResult to be used for the test run.
 */
protected TestResult createTestResult() {
    return new TestResult();
}

public synchronized void addListener(TestListener listener) {
	// protected List<TestListener> fListeners;
        fListeners.add(listener);
    }
// suite.run() fTests中的每一个test 
public void run(TestResult result) {
        for (Test each : fTests) {
            if (result.shouldStop()) {
                break;
            }
            runTest(each, result);
        }
    }
/**
 * Runs the test case and collects the results in TestResult.
 * 调用testResult的run方法
 */
public void run(TestResult result) {
    result.run(this);
}
// 运行test
protected void run(final TestCase test) {
        startTest(test);
        Protectable p = new Protectable() {
            public void protect() throws Throwable {
                test.runBare();//执行runBare方法执行test用例
            }
        };
        runProtected(test, p);

        endTest(test);
    }
public void startTest(Test test) {
        final int count = test.countTestCases();
        synchronized (this) {
            fRunTests += count;
        }
        for (TestListener each : cloneListeners()) {
            each.startTest(test);
        }
    }

public void startTest(Test test) {
        getWriter().print(".");//运行一个则加一个点
        if (fColumn++ >= 40) {
            getWriter().println();
            fColumn = 0;
        }
    }

// 运行一个空的测试序列
public void runBare() throws Throwable {
        Throwable exception = null;
	// 设置装置。比如打开网络连接等，在执行测试之前调用方法。
        setUp();
        try {
	    // 看下面的runTest方法 
            runTest();//执行test
        } catch (Throwable running) {
            exception = running;
        } finally {
            try {
                tearDown();
            } catch (Throwable tearingDown) {
                if (exception == null) exception = tearingDown;
            }
        }
        if (exception != null) throw exception;
    }

protected void runTest() throws Throwable {
        assertNotNull("TestCase.fName cannot be null", fName); // Some VMs crash when calling getMethod(null,null);
        Method runMethod = null;
        try {
            runMethod = getClass().getMethod(fName, (Class[]) null);
        } catch (NoSuchMethodException e) {
            fail("Method \"" + fName + "\" not found");
        }
	// .......... runMethod.invoke(this); 执行方法
     try {
            runMethod.invoke(this);
        } catch (InvocationTargetException e) {
        // 如果方法执行错误，会触发这个异常 会连续被上层捕捉到
            e.fillInStackTrace();
            throw e.getTargetException();
        } catch (IllegalAccessException e) {
            e.fillInStackTrace();
            throw e;
        }
    }

public void runProtected(final Test test, Protectable p) {
    try {
        p.protect();
    } catch (AssertionFailedError e) {
    // 验证失败，添加一条失败信息
        addFailure(test, e);
    } catch (ThreadDeath e) { // don't catch ThreadDeath by accident
        throw e;
    } catch (Throwable e) {
        addError(test, e);
    }
}

public ArrayDeque() {
// 初始化的数组大小是16
        elements = new Object[16];
    }

public ArrayDeque(int numElements) {
        allocateElements(numElements);
    }

public ArrayDeque(Collection<? extends E> c) {
        allocateElements(c.size());
        // addAll方法就是为c 进行for循环添加
        addAll(c);
    }

// 在前面添加元素，也就是在数组的第一个位置上加元素
public void addFirst(E e) {
        if (e == null)
            throw new NullPointerException();
            // 在前面添加的时候，head-1 的位置上插入 e
        elements[head = (head - 1) & (elements.length - 1)] = e;
        if (head == tail)
            doubleCapacity();
    }

public void addLast(E e) {
        if (e == null)
            throw new NullPointerException();
            添加到下一个位置
        elements[tail] = e;
        /* 
         * 如果当前添加位置的下一个位置 与上 长度-1 
         *（因为长度都是2的倍数，所以-1之后，2进制后几位都是1，保证负数的时候也能够找到正确的索引）
         * 如果tail和head相等说明数组满了，需要扩容
         */
        if ( (tail = (tail + 1) & (elements.length - 1)) == head)
            doubleCapacity();
    }

private void doubleCapacity() {
        assert head == tail;
        int p = head;
        int n = elements.length;
        int r = n - p; // head右边元素的个数
        int newCapacity = n << 1; // 扩充为原来的2倍
        if (newCapacity < 0)
            throw new IllegalStateException("Sorry, deque too big");
        Object[] a = new Object[newCapacity]; //创建新数组
        Systkkem.arraycopy(elements, p, a, 0, r); 
        System.arraycopy(elements, 0, a, r, p);// 两部copy数组相当于从 head -> tail 重新排序了
        elements = a;
        head = 0;
        tail = n;
    }

public E remove() {
        return removeFirst();
    }

public E removeFirst() {
        E x = pollFirst();
        if (x == null)
            throw new NoSuchElementException();
        return x;
    }

public E pollFirst() {
        int h = head;
        @SuppressWarnings("unchecked")
        E result = (E) elements[h];
        // Element is null if deque empty
        if (result == null)
            return null;
        elements[h] = null;     // Must null out slot
        // 把element的头部位置置空后，将head向前移
        head = (h + 1) & (elements.length - 1);
        return result;
    }

public Object[] toArray() {
        return copyElements(new Object[size()]);
    }

private <T> T[] copyElements(T[] a) {
        if (head < tail) {
         // 如果顺序正常
            System.arraycopy(elements, head, a, 0, size());
        } else if (head > tail) {
         // 否则将head右侧的先copy到数组中，在copy剩下的
            int headPortionLen = elements.length - head;
            System.arraycopy(elements, head, a, 0, headPortionLen);
            System.arraycopy(elements, 0, a, headPortionLen, tail);
        }
        return a;
   }

public int size() {
         return (tail - head) & (elements.length - 1);
    }

/* 列举简单的行驶工具 */
public enum trafficTool {
    BIKE,CAR,BUS,TRAIN,AIRPLANE
}

public class TrafficToolTest {

    public void chooseTool(TrafficTool trafficTool){
        switch (trafficTool){
            case BIKE:
                System.out.println("自行车");break;
            case CAR:
                System.out.println("汽车");break;
        }
    }

    public static void main(String[] args) {
        TrafficToolTest trafficToolTest = new TrafficToolTest();
        trafficToolTest.chooseTool(TrafficTool.BIKE);
    }
}

SPRING("春天"),SUMMER("夏天"),FALL("秋天"),WINTER("冬天");

private final String name;

SeasonEnum(String name){
    this.name = name;
}
String getName(){
   return name;
}

public enum SeasonEnum {
    SPRING("春天") {
        @Override
        public String comm() {
            return "这是春天";
        }
    },SUMMER("夏天") {
        @Override
        public String comm() {
            return "这是夏天";
        }
    },FALL("秋天") {
        @Override
        public String comm() {
            return "这是冬天";
        }
    },WINTER("冬天") {
        @Override
        public String comm() {
            return "这是冬天";
        }
    };

    private final String name;

    SeasonEnum(String name){
        this.name = name;
    }
    String getName(){
       return name;
    }
    public abstract String comm();
}

/* 简单创建，以后就可以实现枚举类的多种复用 */
EnumMap<SeasonEnum,Integer> enumIntegerEnumMap = new EnumMap<SeasonEnum, Integer>(SeasonEnum.class);
Set<SeasonEnum> set = enumIntegerEnumMap.keySet();
enumIntegerEnumMap.put(SeasonEnum.SPRING,1);
System.out.println(enumIntegerEnumMap.get(SeasonEnum.SPRING));

/* 可以看到hashSet的这几个构造方法和HashMap息息相关 */
private transient HashMap<E,Object> map;
public HashSet() {
    map = new HashMap<>();
}

public HashSet(Collection<? extends E> c) {
    map = new HashMap<>(Math.max((int) (c.size()/.75f) + 1, 16));
    addAll(c);
}

public HashSet(int initialCapacity, float loadFactor) {
    map = new HashMap<>(initialCapacity, loadFactor);
}

public HashSet(int initialCapacity) {
    map = new HashMap<>(initialCapacity);
}

HashSet(int initialCapacity, float loadFactor, boolean dummy) {
    map = new LinkedHashMap<>(initialCapacity, loadFactor);
}

public boolean add(E e) {
  /* 这里的PRESENT等于new Object() */
       return map.put(e, PRESENT)==null;
   }

public Iterator<E> iterator() {
    return map.keySet().iterator();
}

public boolean contains(Object o) {
    return map.containsKey(o);
}

/* 其实大致和HashMap是类似的也是使用Entry作为基本结构 */
public synchronized V put(K key, V value) {
     // Make sure the value is not null
     if (value == null) {
         throw new NullPointerException();
     }
     // Makes sure the key is not already in the hashtable.
     Entry<?,?> tab[] = table;
     int hash = key.hashCode();
     /* 这里的0x7FFFFFFF 是32-bit的int的最大值 */
     int index = (hash & 0x7FFFFFFF) % tab.length;
     @SuppressWarnings("unchecked")
     Entry<K,V> entry = (Entry<K,V>)tab[index];
     /* 如果这个entry存在，也就是键值重复 */
     for(; entry != null ; entry = entry.next) {
         if ((entry.hash == hash) && entry.key.equals(key)) {
             V old = entry.value;
             entry.value = value;
             return old;
         }
     }
    /* 否则添加Entry节点 */
     addEntry(hash, key, value, index);
     return null;
 }

 private void addEntry(int hash, K key, V value, int index) {
    modCount++;

    Entry<?,?> tab[] = table;
    if (count >= threshold) {
      /* 如果当前count大于阈值的大小 重新生成table size和hash值 */
        // Rehash the table if the threshold is exceeded
        rehash();

        tab = table;
        hash = key.hashCode();
        index = (hash & 0x7FFFFFFF) % tab.length;
    }

    // Creates the new entry.
    @SuppressWarnings("unchecked")
    Entry<K,V> e = (Entry<K,V>) tab[index];
    tab[index] = new Entry<>(hash, key, value, e);
    count++;
}

static class Node<K,V> implements Map.Entry<K,V> {
    final int hash;
    final K key;
    V value;
    // 指向下一节点的指针
    Node<K,V> next;
    Node(int hash, K key, V value, Node<K,V> next) {
        this.hash = hash;
        this.key = key;
        this.value = value;
        this.next = next;
    }

    public final K getKey()        { return key; }
    public final V getValue()      { return value; }
    public final String toString() { return key + "=" + value; }

    public final int hashCode() {
        return Objects.hashCode(key) ^ Objects.hashCode(value);
    }

    public final V setValue(V newValue) {
        V oldValue = value;
        value = newValue;
        return oldValue;
    }

    public final boolean equals(Object o) {
        if (o == this)
            return true;
        if (o instanceof Map.Entry) {
            Map.Entry<?,?> e = (Map.Entry<?,?>)o;
            if (Objects.equals(key, e.getKey()) &&
                Objects.equals(value, e.getValue()))
                return true;
        }
        return false;
    }
}

/* 实际上结构就是一个类型为Node的数组,使用transient 防止对整个table全部序列化 */
transient Node<K,V>[] table;

/**
 * Holds cached entrySet(). Note that AbstractMap fields are used
 * for keySet() and values().
 * 得到entryset
 */
transient Set<Map.Entry<K,V>> entrySet;

/**
 * The number of key-value mappings contained in this map.
   map的大小
 */
transient int size;

/* 操作次数 */
transient int modCount;

/* 阈值，如果超过临界值就会自动扩充数组 */
int threshold;

/* 加载因子  */
final float loadFactor;

/* 第一个参数 是默认的初始化阈值大小，第二个是加载因子大小 */
public HashMap(int initialCapacity, float loadFactor) {
    if (initialCapacity < 0)
    /* 如果制定的初始化阈值小于0 */
        throw new IllegalArgumentException("Illegal initial capacity: " +
                                           initialCapacity);
    if (initialCapacity > MAXIMUM_CAPACITY)
        initialCapacity = MAXIMUM_CAPACITY;
    if (loadFactor <= 0 || Float.isNaN(loadFactor))
        throw new IllegalArgumentException("Illegal load factor: " +
                                           loadFactor);
    this.loadFactor = loadFactor;
    this.threshold = tableSizeFor(initialCapacity);
}

/* 使用this调用上面的方法 */
public HashMap(int initialCapacity) {
    this(initialCapacity, DEFAULT_LOAD_FACTOR);
}

/**
 * 使用默认的阈值和因子，大小分别为16和0.75
 * Constructs an empty <tt>HashMap</tt> with the default initial capacity
 * (16) and the default load factor (0.75).
 */
public HashMap() {
    this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
}

public V put(K key, V value) {
  /* 调用putVal方法 */
    return putVal(hash(key), key, value, false, true);
}
/**
 * Implements Map.put and related methods
 *
 * @param hash hash for key key的hash码
 * @param key the key key值
 * @param value the value to put value值
 * @param onlyIfAbsent if true, don't change existing value 如果是true 不改变当前值
 * @param evict if false, the table is in creation mode. 如果是false，那么table就属于创建模式 （？）
 * @return previous value, or null if none
 */
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
               boolean evict) {
    Node<K,V>[] tab; Node<K,V> p; int n, i;
    /* 当Map为空的时候  这时候tab为16也就是n为16*/
    /* 这是当map中的内容为空的时候
     * newCap = DEFAULT_INITIAL_CAPACITY;
     * newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
    */
    if ((tab = table) == null || (n = tab.length) == 0)
        n = (tab = resize()).length;
    /* 如果当前tab的length&hash值再tab列表中不重复 */
    if ((p = tab[i = (n - 1) & hash]) == null)
    /* 新建一个noede 再tab[i]的位置上 */
        tab[i] = newNode(hash, key, value, null);
    else {
        Node<K,V> e; K k;
        /* 当添加重复的key的时候 这时候hash和key的值都相等，就相当于不添加 */
        if (p.hash == hash &&
            ((k = p.key) == key || (key != null && key.equals(k))))
            e = p;
        else if (p instanceof TreeNode)
        /* 如果e是treeNode的时候  */
            e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
        else {
            for (int binCount = 0; ; ++binCount) {
                if ((e = p.next) == null) {
                // 将新值添加到p的后面
                    p.next = newNode(hash, key, value, null);
                    if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                    /* 如果当前列表中的长度大于等于 8-1 的时候，把这个列表整理成树形结构 */
                        treeifyBin(tab, hash);
                    break;
                }
                if (e.hash == hash &&
                    ((k = e.key) == key || (key != null && key.equals(k))))
                    break;
                p = e;
            }
        }
        if (e != null) { // existing mapping for key
            V oldValue = e.value;
            if (!onlyIfAbsent || oldValue == null)
                e.value = value;
            afterNodeAccess(e);
            return oldValue;
        }
    }
    ++modCount;
    /* 如果当前size大于threshold的时候扩充table */
    if (++size > threshold)
        resize();
    afterNodeInsertion(evict);
    return null;
}

final Node<K,V>[] resize() {
        Node<K,V>[] oldTab = table;
        int oldCap = (oldTab == null) ? 0 : oldTab.length;
        int oldThr = threshold;
        int newCap, newThr = 0;
        if (oldCap > 0) {
            if (oldCap >= MAXIMUM_CAPACITY) {
                threshold = Integer.MAX_VALUE;
                return oldTab;
            } //newcap是oldcap的2倍
            else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
                     oldCap >= DEFAULT_INITIAL_CAPACITY)
                newThr = oldThr << 1; // double threshold
        }
        else if (oldThr > 0) // initial capacity was placed in threshold
            newCap = oldThr;
        else {               // zero initial threshold signifies using defaults
            newCap = DEFAULT_INITIAL_CAPACITY;
            newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
        }
        if (newThr == 0) {
            float ft = (float)newCap * loadFactor;
            newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
                      (int)ft : Integer.MAX_VALUE);
        }
        threshold = newThr;
        @SuppressWarnings({"rawtypes","unchecked"})
        Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
        table = newTab;
        if (oldTab != null) {
        //循环原table数组 ？因为在扩容后 hash & (size-1) 的位置发生了变化 ，所以应当进行重排
            for (int j = 0; j < oldCap; ++j) { 
                Node<K,V> e;
                if ((e = oldTab[j]) != null) {
                    oldTab[j] = null;
                    if (e.next == null)//说明e不存在hash冲突
                        newTab[e.hash & (newCap - 1)] = e;
                    else if (e instanceof TreeNode)
                        ((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
                    else { // preserve order
                        Node<K,V> loHead = null, loTail = null;
                        Node<K,V> hiHead = null, hiTail = null;
                        Node<K,V> next;
                        do { //再去循环bin
                            next = e.next;
                            if ((e.hash & oldCap) == 0) { //如果在低位 （老）数组中也就是元素hast和就数组取模为0时，说明重排后仍在老数组内
                                if (loTail == null)
                                    loHead = e;
                                else
                                    loTail.next = e;
                                loTail = e;//递归向下继续排
                            }
                            else {//否则在高位数组中 ，也就是在扩容出来的数组中
                                if (hiTail == null)
                                    hiHead = e;
                                else
                                    hiTail.next = e;
                                hiTail = e;
                            }
                        } while ((e = next) != null);
                        if (loTail != null) {
                            loTail.next = null;
                            newTab[j] = loHead; //低位数组还是在原来的位置上
                        }
                        if (hiTail != null) {
                            hiTail.next = null;
                            newTab[j + oldCap] = hiHead; //高位数组在旧数组+j的位置上
                        }
                    }
                }
            }
        }
        return newTab;
    }

public V get(Object key) {
    Node<K,V> e;
    return (e = getNode(hash(key), key)) == null ? null : e.value;
}

final Node<K,V> getNode(int hash, Object key) {
    Node<K,V>[] tab; Node<K,V> first, e; int n; K k;
    if ((tab = table) != null && (n = tab.length) > 0 &&
        (first = tab[(n - 1) & hash]) != null) {
        if (first.hash == hash && // 先回检查第一个节点
            ((k = first.key) == key || (key != null && key.equals(k))))
            return first;
        if ((e = first.next) != null) {
            if (first instanceof TreeNode)
                return ((TreeNode<K,V>)first).getTreeNode(hash, key);
            do {
              /* 从第二个节点开始循环 查找hash和key分别相同  */
                if (e.hash == hash &&
                    ((k = e.key) == key || (key != null && key.equals(k))))
                    return e;
            } while ((e = e.next) != null);
        }
    }
    return null;
}

public V remove(Object key) {
    Node<K,V> e;
    return (e = removeNode(hash(key), key, null, false, true)) == null ?
        null : e.value;
}
/**
 * Implements Map.remove and related methods
 *
 * @param hash key的hash值
 * @param key 键值
 * @param value 如果想匹配的话就是value，否则空
 * @param matchValue 如果是ture那么就移除和value equal的
 * @param movable 如果是false的话，移除这个节点不要移动其他节点
 * @return the node, or null if none
 */
final Node<K,V> removeNode(int hash, Object key, Object value,
                           boolean matchValue, boolean movable) {
    Node<K,V>[] tab; Node<K,V> p; int n, index;
    /* 确定节点 */
    if ((tab = table) != null && (n = tab.length) > 0 &&
        (p = tab[index = (n - 1) & hash]) != null) {
        Node<K,V> node = null, e; K k; V v;
        /* 如果hash值相同 key值也相同 说明就是这个节点 */
        if (p.hash == hash &&
            ((k = p.key) == key || (key != null && key.equals(k))))
            node = p;
        else if ((e = p.next) != null) {
          /* 否则横向查找下一个节点 */
            if (p instanceof TreeNode)
                node = ((TreeNode<K,V>)p).getTreeNode(hash, key);
            else {
                do {
                    /* 省略-------- */
                } while ((e = e.next) != null);
            }
        }
        if (node != null && (!matchValue || (v = node.value) == value ||
                             (value != null && value.equals(v)))) {
            if (node instanceof TreeNode)
                ((TreeNode<K,V>)node).removeTreeNode(this, tab, movable);
                /* 接下来把tab中对应的index remove掉 */
            else if (node == p)
                tab[index] = node.next;
            else
                p.next = node.next;
            ++modCount;
            --size;
            afterNodeRemoval(node);
            return node;
        }
    }
    return null;
}

final class KeySet extends AbstractSet<K> {
    public final int size()                 { return size; } //返回当前size
    public final void clear()               { HashMap.this.clear(); } //直接调用hashMap的clear方法
    public final Iterator<K> iterator()     { return new KeyIterator(); }
    public final boolean contains(Object o) { return containsKey(o); }
    public final boolean remove(Object key) {
        return removeNode(hash(key), key, null, false, true) != null;
    }
    public final Spliterator<K> spliterator() {
        return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0);
    }
    public final void forEach(Consumer<? super K> action) {
        Node<K,V>[] tab;
        if (action == null)
            throw new NullPointerException();
        if (size > 0 && (tab = table) != null) {
            int mc = modCount;
            /* 把当前操作数记下来  */
            for (int i = 0; i < tab.length; ++i) {
                for (Node<K,V> e = tab[i]; e != null; e = e.next)
                    action.accept(e.key);
            }
            if (modCount != mc)
                throw new ConcurrentModificationException();
        }
    }
}

/* LinkedList的内部变量 可以看出LinkedList其实就是一个链表 */
transient int size = 0;

/**
 * 指向首节点
 * Invariant: (first == null && last == null) ||
 *            (first.prev == null && first.item != null)
 */
transient Node<E> first;

/**
 * 指向尾节点
 * Invariant: (first == null && last == null) ||
 *            (last.next == null && last.item != null)
 */
transient Node<E> last;

/* 内部node实现 */
    E item;
    Node<E> next;
    Node<E> prev;
/* 双向链表 */
    Node(Node<E> prev, E element, Node<E> next) {
        this.item = element;
        this.next = next;
        this.prev = prev;
    }
}

/* 空构造函数 比较常用 */
public LinkedList() {
   }

/* 有collection参数的构造函数 */
public LinkedList(Collection<? extends E> c) {
    this();
    addAll(c);
}

public boolean addAll(Collection<? extends E> c) {
    return addAll(size, c);
}
/* 参数：当前数量也就是要得到当前链表的位置 */
public boolean addAll(int index, Collection<? extends E> c) {
    checkPositionIndex(index);

    Object[] a = c.toArray();
    int numNew = a.length;
    if (numNew == 0)
        return false;
    Node<E> pred, succ;
    // 对插入前情况的判断
    if (index == size) {
//          如果在尾部插入 pred=最后一个节点
        succ = null;
        pred = last;
    } else {
//          否则在中部插入 succ=当前节点 pred=前一节点
/* - - - - - - - - -  */
/*     ^ ^ */
/*     1 2  如果想在2位置插入元素，前一个元素不动，将后面的元素后移*/
        succ = node(index);
        pred = succ.prev;
    }
    for (Object o : a) {
        @SuppressWarnings("unchecked") E e = (E) o;
// 构造方法 前节点/内容/后节点 始终pred是前置节点
        Node<E> newNode = new Node<>(pred, e, null);
        if (pred == null)
// 如果pred==null 说明 本身列表开始就是空的或者在开头插入元素
            first = newNode;
        else
// 否则在后面插入newNode
            pred.next = newNode;
// 向后循环节点
        pred = newNode;
    }
// 如果succ==null 说明到最后一个节点后位置 
// 将最后的新插入的元素pred赋值给last
    if (succ == null) {
        last = pred;
    } else {
      /* 否则插入在succ前 */
        pred.next = succ;
        succ.prev = pred;
    }

    size += numNew;
    modCount++;
    return true;
}

/* add方法默认调用linklast方法，也就是向后添加元素 */
public boolean add(E e) {
    linkLast(e);
    return true;
}

/* 同样有addLast 达到相同的目的，就是不返回任何东西 */
public void addLast(E e) {
        linkLast(e);
    }

void linkLast(E e) {
    final Node<E> l = last;
    /* 获得最后一个元素当作新节点的前置节点 */
    final Node<E> newNode = new Node<>(l, e, null);
    /* 把当前节点付给last */
    last = newNode;
    if (l == null)
        first = newNode;
    else
    // 将last的next指向新节点,完成双方相互链接
        l.next = newNode;
    size++;
    modCount++;
}

public void addFirst(E e) {
    linkFirst(e);
}

private void linkFirst(E e) {
    // 获取首节点
    final Node<E> f = first;
    // 设置新节点
    final Node<E> newNode = new Node<>(null, e, f);
    //设置新节点为首节点
    first = newNode;
    if (f == null)
        last = newNode;
    else
    // 将新节点与原首节点连接
        f.prev = newNode;
    size++;
    modCount++;
}

public E remove(int index) {
  /* 先判断是否越界 */
      checkElementIndex(index);
      return unlink(node(index));
  }

E unlink(Node<E> x) {
    // assert x != null;
    final E element = x.item;
    final Node<E> next = x.next;
    final Node<E> prev = x.prev;
/* 如果prev是空 说明当前元素是第一个元素 如 A B C 移除A，直接将B指向首节点即可 */
    if (prev == null) {
        first = next;
    } else {
      /* 当前节点与前后节点断绝链接 如ABC移除B，则需要将A.next指向C，B.pre指向空 */
        prev.next = next;
        x.prev = null;
    }
    // 因为LinkedList为双向链表，需要取消next和prev
/* 如果是最后一个元素 */
    if (next == null) {
        last = prev;
    } else {
      /* 当前节点与前后节点断绝链接 因为LinkedList是双向链表 */
        next.prev = prev;
        x.next = null;
    }
/* 置空 */
    x.item = null; 
    size--;
    modCount++;
    return element;
}

public E removeFirst() {
    final Node<E> f = first;
    if (f == null)
        throw new NoSuchElementException();
    return unlinkFirst(f);
}

private E unlinkFirst(Node<E> f) {
    // assert f == first && f != null;
    final E element = f.item;
    final Node<E> next = f.next;
    f.item = null;
    f.next = null; // help GC
    first = next;
    if (next == null)
        last = null;
    else
        next.prev = null;
    size--;
    modCount++;
    return element;
}

public E get(int index) {
    checkElementIndex(index);
    /* 得到index处节点的item信息 */
    return node(index).item;
}

Node<E> node(int index) {
        // assert isElementIndex(index);
        // 分两个方向查找，1.如果给定的index小于size的一半
    if (index < (size >> 1)) {
        Node<E> x = first;
        //从头开始
        for (int i = 0; i < index; i++)
            x = x.next;
            // 返回最后一个
        return x;
    } else {
    // 2.如果给定的index大于size的一半
        Node<E> x = last;
        // 从尾部开始找
        for (int i = size - 1; i > index; i--)
            x = x.prev;
            //返回最后的那个
        return x;
    }
}

public E set(int index, E element) {
    checkElementIndex(index);
    Node<E> x = node(index);
    E oldVal = x.item;
    x.item = element;
    /* set方法会返回原来的值 */
    return oldVal;
}

/**
 * Retrieves, but does not remove, the head (first element) of this list.
 * 只是检索栈首元素，但并不弹出
 * @return the head of this list, or {@code null} if this list is empty
 * @since 1.5
 */
public E peek() {
    final Node<E> f = first;
    return (f == null) ? null : f.item;
}

/**
 * Retrieves and removes the head (first element) of this list.
 * 检索并且移除栈首元素 unlinkFirst是可以返回移除元素的
 * @return the head of this list, or {@code null} if this list is empty
 * @since 1.5
 */
public E poll() {
    final Node<E> f = first;
    return (f == null) ? null : unlinkFirst(f);
}

/**
 * Pushes an element onto the stack represented by this list.  In other
 * words, inserts the element at the front of this list.
 * 在栈首堆一个元素
 * <p>This method is equivalent to {@link #addFirst}.
 *
 * @param e the element to push
 * @since 1.6
 */
public void push(E e) {
    addFirst(e);
}

/**
 * Pops an element from the stack represented by this list.  In other
 * words, removes and returns the first element of this list.
 * 出栈
 * <p>This method is equivalent to {@link #removeFirst()}.
 *
 * @return the element at the front of this list (which is the top
 *         of the stack represented by this list)
 * @throws NoSuchElementException if this list is empty
 * @since 1.6
 */
public E pop() {
    return removeFirst();
}

for (int i=0; i<size; i++) {
    s.writeObject(elementData[i]);
}

/* 没有参数的情况下 */
public ArrayList() {
    // 设置默认的内容为{}
    this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/* 默认是拥有默认容量（10）的空的 array list */
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/* 这个默认的容量是定义好的10  */
 private static final int DEFAULT_CAPACITY = 10;

/* 当参数是容量的大小的时候  */
 public ArrayList(int initialCapacity) {
    if (initialCapacity > 0) {
      /* 如果自定义初始容量大小*/
        this.elementData = new Object[initialCapacity];
    } else if (initialCapacity == 0) {
        this.elementData = EMPTY_ELEMENTDATA;
    } else {
      /* 如果参数小于0 报参数异常的错误（IllegalArgumentException） */
        throw new IllegalArgumentException("Illegal Capacity: "+
                                           initialCapacity);
    }
}
/* 当参数是一个Collection结构的时候 */
public ArrayList(Collection<? extends E> c) {
     elementData = c.toArray();
     if ((size = elementData.length) != 0) {
         // c.toArray might (incorrectly) not return Object[] (see 6260652)
         if (elementData.getClass() != Object[].class)
         /* 如果不是object类型的话 转换成object类型 */
             elementData = Arrays.copyOf(elementData, size, Object[].class);
     } else {
         // replace with empty array.
         this.elementData = EMPTY_ELEMENTDATA;
     }
 }