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Java核心类库源码全解析，掌握JDK集合框架核心技术

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Java作为一门广泛应用于企业级应用开发的语言，其核心类库提供了丰富的API，极大地简化了编程工作。其中，JDK集合框架是Java核心类库的重要组成部分，它提供了强大的数据结构和算法支持。本文将深入解析Java核心类库源码，特别是JDK集合框架的核心技术，帮助读者全面掌握。

1. Java核心类库概述

Java核心类库是指Java标准库（Java Standard Edition API），它包含了Java编程语言中几乎所有常用的类和接口。这些类和接口被组织在多个包中，例如：

  • java.lang：包含Java语言的核心类，如Object、String、System等。
  • java.util：提供集合框架、日期和时间处理、国际化和数学运算等功能。
  • java.io：提供文件输入/输出操作、序列化等。
  • java.net：提供网络通信功能，如URL、Socket等。

2. 集合框架概述

JDK集合框架是一个用于存储和操作对象的框架，它提供了多种数据结构，如列表、集合、映射和队列。集合框架的核心接口包括：

  • Collection：集合的根接口，表示一组对象。
  • List：有序集合，允许重复元素。
  • Set：无序集合，不允许重复元素。
  • Queue：队列，用于元素先进先出（FIFO）的操作。
  • Map：键值对映射，将键映射到值。

3. 集合框架核心技术解析

3.1. 集合框架实现类

Java集合框架提供了多种实现类，如ArrayList、LinkedList、HashSet、TreeSet、HashMap、TreeMap等。以下是对这些实现类的源码解析：

3.1.1. ArrayList

ArrayList是基于动态数组实现的，它提供了快速的随机访问能力。以下是ArrayList的核心方法：

public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable {
    private static final long serialVersionUID = 8683452581122892189L;

    private static final int DEFAULT_CAPACITY = 10;

    private transient Object[] elementData;

    private int size;

    public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ARRAY;
    }

    public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
            this.elementData = EMPTY_ARRAY;
        } else {
            throw new IllegalArgumentException("Illegal Capacity: " + initialCapacity);
        }
    }

    public boolean add(E e) {
        modCount++;
        ensureCapacityInternal(size + 1);
        elementData[size++] = e;
        return true;
    }

    private void ensureCapacityInternal(int minCapacity) {
        if (elementData == DEFAULTCAPACITY_EMPTY_ARRAY) {
            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
        }

        ensureExplicitCapacity(minCapacity);
    }

    private void ensureExplicitCapacity(int minCapacity) {
        if (minCapacity - elementData.length > 0) {
            grow(minCapacity);
        }
    }

    private void grow(int minCapacity) {
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
        if (newCapacity - minCapacity < 0) {
            newCapacity = minCapacity;
        }
        if (newCapacity - MAX_ARRAY_SIZE > 0) {
            newCapacity = hugeCapacity(minCapacity);
        }
        elementData = Arrays.copyOf(elementData, newCapacity);
    }

    private static int hugeCapacity(int minCapacity) {
        if (minCapacity < 0) {
            throw new OutOfMemoryError();
        }
        return (minCapacity > MAX_ARRAY_SIZE) ? Integer.MAX_VALUE : MAX_ARRAY_SIZE;
    }

    public E get(int index) {
        rangeCheck(index);

        return (E) elementData[index];
    }

    public E set(int index, E element) {
        rangeCheck(index);

        E oldValue = (E) elementData[index];
        elementData[index] = element;

        return oldValue;
    }

    public int indexOf(Object o) {
        if (o == null) {
            for (int i = 0; i < size; i++) {
                if (elementData[i] == null) {
                    return i;
                }
            }
        } else {
            for (int i = 0; i < size; i++) {
                if (o.equals(elementData[i])) {
                    return i;
                }
            }
        }
        return -1;
    }

    public int lastIndexOf(Object o) {
        if (o == null) {
            for (int i = size - 1; i >= 0; i--) {
                if (elementData[i] == null) {
                    return i;
                }
            }
        } else {
            for (int i = size - 1; i >= 0; i--) {
                if (o.equals(elementData[i])) {
                    return i;
                }
            }
        }
        return -1;
    }

    public void add(int index, E element) {
        rangeCheckForAdd(index);

        ensureCapacityInternal(size + 1);
        System.arraycopy(elementData, index, elementData, index + 1, size - index);

        elementData[index] = element;
        size++;
    }

    public E remove(int index) {
        rangeCheck(index);

        modCount++;
        E oldValue = (E) elementData[index];

        int numMoved = size - index - 1;
        if (numMoved > 0) {
            System.arraycopy(elementData, index + 1, elementData, index, numMoved);
        }
        elementData[--size] = null;

        return oldValue;
    }

    public boolean remove(Object o) {
        if (o == null) {
            for (int index = 0; index < size; index++) {
                if (elementData[index] == null) {
                    fastRemove(index);
                    return true;
                }
            }
        } else {
            for (int index = 0; index < size; index++) {
                if (o.equals(elementData[index])) {
                    fastRemove(index);
                    return true;
                }
            }
        }
        return false;
    }

    private void fastRemove(int index) {
        modCount++;
        int numMoved = size - index - 1;
        if (numMoved > 0) {
            System.arraycopy(elementData, index + 1, elementData, index, numMoved);
        }
        elementData[--size] = null;
    }

    public boolean addAll(int index, Collection<? extends E> c) {
        rangeCheckForAdd(index);

        Object[] a = c.toArray();
        int numNew = a.length;
        ensureCapacityInternal(size + numNew);

        int numMoved = size - index;
        if (numMoved > 0) {
            System.arraycopy(elementData, index, elementData, index + numNew, numMoved);
        }
        System.arraycopy(a, 0, elementData, index, numNew);
        size += numNew;

        return numNew != 0;
    }

    public boolean removeAll(Collection<?> c) {
        Objects.requireNonNull(c);
        modCount++;
        int len = size;
        for (int i = 0; i < len; i++) {
            if (c.contains(elementData[i])) {
                fastRemove(i);
                i--;
                len--;
            }
        }
        return len != size;
    }

    public boolean retainAll(Collection<?> c) {
        Objects.requireNonNull(c);
        modCount++;
        int len = size;
        for (int i = 0; i < len; i++) {
            if (!c.contains(elementData[i])) {
                fastRemove(i);
                i--;
                len--;
            }
        }
        return len != size;
    }

    public void clear() {
        modCount++;
        for (int i = 0; i < size; i++) {
            elementData[i] = null;
        }
        size = 0;
    }

    public Object clone() {
        try {
            ArrayList<?> v = (ArrayList<?>) super.clone();
            v.elementData = Arrays.copyOf(elementData, size);
            return v;
        } catch (CloneNotSupportedException e) {
            throw new InternalError(e);
        }
    }

    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof ArrayList)) {
            return false;
        }
        ArrayList<?> that = (ArrayList<?>) o;
        if (size != that.size()) {
            return false;
        }
        Object[] elementData1 = elementData;
        Object[] elementData2 = that.elementData;
        for (int i = 0; i < size; i++) {
            if (!Objects.equals(elementData1[i], elementData2[i])) {
                return false;
            }
        }
        return true;
    }

    public int hashCode() {
        int h = 1;
        int size = size;
        for (int i = 0; i < size; i++) {
            Object o = elementData[i];
            if (o != null) {
                h = 31 * h + o.hashCode();
            }
        }
        return h;
    }

    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append('[');
        for (int i = 0; i < size; i++) {
            if (i > 0) {
                sb.append(", ");
            }
            Object o = elementData[i];
            sb.append(o == this ? "(this Collection)" : o);
        }
        sb.append(']');
        return sb.toString();
    }

    private void rangeCheck(int index) {
        if (index >= size || index < 0) {
            throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
        }
    }

    private void rangeCheckForAdd(int index) {
        if (index > size || index < 0) {
            throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
        }
    }

    public Iterator<E> iterator() {
        return new Itr();
    }

    private class Itr implements Iterator<E> {
        int cursor;       // index of next element to return
        int lastRet = -1; // index of last returned element
        int expectedModCount = modCount;

        public boolean hasNext() {
            return cursor != size;
        }

        public E next() {
            checkForComodification();
            int i = cursor;
            if (i >= size) {
                throw new NoSuchElementException();
            }
            Object[] elementData = ArrayList.this.elementData;
            if (i >= elementData.length) {
                throw new ConcurrentModificationException();
            }
            E x = (E) elementData[i];
            cursor = i + 1;
            lastRet = i;
            return x;
        }

        public void remove() {
            checkForComodification();

            int lastRet = this.lastRet;
            if (lastRet == -1) {
                throw new IllegalStateException();
            }

            try {
                ArrayList.this.remove(lastRet);
                cursor = lastRet;
                lastRet = -1;
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException e) {
                throw new ConcurrentModificationException();
            }
        }

        final void checkForComodification() {
            if (modCount != expectedModCount) {
                throw new ConcurrentModificationException();
            }
        }
    }

    public ListIterator<E> listIterator(int index) {
        if (index < 0 || index > size) {
            throw new IndexOutOfBoundsException("Index: " + index);
        }
        return new ListItr(index);
    }

    private class ListItr extends Itr implements ListIterator<E> {
        ListItr(int index) {
            super();
            cursor = index;
        }

        public boolean hasPrevious() {
            return cursor > 0;
        }

        public E previous() {
            checkForComodification();
            int i = cursor - 1;
            if (i < 0) {
                throw new NoSuchElementException();
            }
            Object[] elementData = ArrayList.this.elementData;
            if (i >= elementData.length) {
                throw new ConcurrentModificationException();
            }
            E x = (E) elementData[i];
            cursor = i;
            lastRet = i;
            return x;
        }

        public int nextIndex() {
            return cursor;
        }

        public int previousIndex() {
            return cursor - 1;
        }

        public void set(E e) {
            if (lastRet < 0) {
                throw new IllegalStateException();
            }
            checkForComodification();

            try {
                ArrayList.this.set(lastRet, e);
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }

        public void add(E e) {
            checkForComodification();
            try {
                int i = lastRet + 1;
                ArrayList.this.add(i, e);
                cursor = i;
                lastRet = -1;
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }
    }

    public List<E> subList(int fromIndex, int toIndex) {
        subListRangeCheck(fromIndex, toIndex, size);
        return new SubList<>(this, fromIndex, toIndex);
    }

    private void subListRangeCheck(int fromIndex, int toIndex, int size) {
        if (fromIndex < 0) {
            throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
        }
        if (toIndex > size) {
            throw new IndexOutOfBoundsException("toIndex = " + toIndex);
        }
        if (fromIndex > toIndex) {
            throw new IllegalArgumentException("fromIndex(" + fromIndex + ") > toIndex(" + toIndex + ")");
        }
    }

    static final class SubList<E> extends AbstractList<E> implements RandomAccess {
        private final ArrayList<E> l;
        private final int offset;
        private final int size;

        SubList(ArrayList<E> l, int fromIndex, int toIndex) {
            this.l = l;
            this.offset = fromIndex;
            this.size = toIndex - fromIndex;
            this.modCount = l.modCount;
        }

        public E get(int index) {
            rangeCheck(index);

            E e = l.get(offset + index);
            this.modCount = l.modCount;
            return e;
        }

        public E set(int index, E e) {
            rangeCheck(index);

            E oldValue = l.set(offset + index, e);
            this.modCount = l.modCount;
            return oldValue;
        }

        public int size() {
            return size;
        }

        public void add(int index, E e) {
            rangeCheckForAdd(index);

            l.add(offset + index, e);
            this.modCount = l.modCount;
        }

        public E remove(int index) {
            rangeCheck(index);

            E oldValue = l.remove(offset + index);
            this.modCount = l.modCount;
            return oldValue;
        }

        public boolean addAll(int index, Collection<? extends E> c) {
            rangeCheckForAdd(index);

            int cSize = c.size();
            if (cSize == 0) {
                return false;
            }

            l.addAll(offset + index, c);
            this.modCount = l.modCount;
            return true;
        }

        public boolean remove(Object o) {
            int i = indexOf(o);
            if (i >= 0) {
                remove(i);
                return true;
            }
            return false;
        }

        public boolean contains(Object o) {
            return indexOf(o) >= 0;
        }

        public Iterator<E> iterator() {
            return listIterator();
        }

        public ListIterator<E> listIterator() {
            return listIterator(0);
        }

        public ListIterator<E> listIterator(int index) {
            return new ListItr(index);
        }

        public List<E> subList(int fromIndex, int toIndex) {
            return l.subList(fromIndex + offset, toIndex + offset);
        }

        private void rangeCheck(int index) {
            if (index < 0 || index >= size) {
                throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
            }
        }

        private void rangeCheckForAdd(int index) {
            if (index < 0 || index > size) {
                throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
            }
        }

        private void checkForComodification() {
            if (modCount != l.modCount) {
                throw new ConcurrentModificationException();
            }
        }
    }
}

3.1.2. LinkedList

LinkedList是基于双向链表实现的，它提供了高效的插入和删除操作。以下是LinkedList的核心方法：

”`java public class LinkedList extends AbstractSequentialList implements List, Deque, Cloneable, java.io.Serializable {

private static final long serialVersionUID = 8683452581122892189L;

transient int size = 0;

transient Node<E> first;

transient Node<E> last;

public LinkedList() {
}

public LinkedList(Collection<? extends E> c) {
    this();
    addAll(c);
}

public boolean add(E e) {
    linkLast(e);
    return true;
}

public void add(int index, E element) {
    checkPositionIndex(index);

    if (index == size) {
        linkLast(element);
    } else {
        linkBefore(element, node(index));
    }
}

public boolean addAll(Collection<? extends E> c) {
    return addAll(size, c);
}

public boolean addAll(int index, Collection<? extends E> c) {
    checkPositionIndex(index);

    Object[] a = c.toArray();
    int numNew = a.length;
    if (numNew == 0) {
        return false;
    }

    int i = index;
    Node<E> succ;
    for (Object e : a) {
        succ = node(i);
        linkBefore((E) e, succ);
        i++;
    }
    return true;
}

public boolean remove(Object o) {
    if (o == null) {
        for (Node<E> x = first; x != null; x = x.next) {
            if (x.item == null) {
                unlinkFirst(x);
                return true;
            }
        }
    } else {
        for (Node<E> x = first; x != null; x = x.next) {
            if (o.equals(x.item)) {
                unlink(x);
                return true;
            }
        }
    }
    return false;
}

public E remove(int index) {
    checkElementIndex(index);
    return unlink(node(index));
}

public boolean removeAll(Collection<?> c) {
    Objects.requireNonNull(c);
    boolean modified = false;
    for (
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