JAVA面试13-List

Vector线程安全的 内部是数组 初始大小为10

线程安全

 public synchronized boolean add(E e) 

public synchronized E remove(int index)
  

初始大小为10

public Vector() {
        this(10);
    }
public Vector(int initialCapacity) {
        this(initialCapacity, 0);
    }
public Vector(int initialCapacity, int capacityIncrement) {
        super();
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        this.elementData = new Object[initialCapacity];
        this.capacityIncrement = capacityIncrement;
    }
 protected Object[] elementData;
 

新增1倍

 private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + ((capacityIncrement > 0) ?capacityIncrement : oldCapacity);
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        elementData = Arrays.copyOf(elementData, newCapacity);
    }

示例

public class T19 {
    public static void main(String[] args) {
        Vector vector=new Vector();
        vector.add("xixi");
        vector.add("lili");
        vector.add("cici");
        vector.remove("xixi");
        System.out.println(vector);  //[lili, cici]
    }
}

toString()

public synchronized String toString() {
        return super.toString();
    }

public String toString() {
        Iterator<E> it = iterator();
        if (! it.hasNext())
            return "[]";

        StringBuilder sb = new StringBuilder();
        sb.append('[');
        for (;;) {
            E e = it.next();
            sb.append(e == this ? "(this Collection)" : e);
            if (! it.hasNext())
                return sb.append(']').toString();
            sb.append(',').append(' ');
        }
    }

ArrayList 非线程安全的 内部是数组

非线程安全的

 public boolean add(E e) 

 public boolean remove(Object o) 

内部是数组

 public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }
  transient Object[] elementData；
  private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

初始大小

/**
     * Default initial capacity.
     */
    private static final int DEFAULT_CAPACITY = 10;

新增0.5倍

 private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        // minCapacity is usually close to size, so this is a win:
        elementData = Arrays.copyOf(elementData, newCapacity);
    }

示例

import java.util.ArrayList;
public class T19 {
    public static void main(String[] args) {
        ArrayList arrayList=new ArrayList();
        arrayList.add("xixi");
        arrayList.add("lili");
        arrayList.add("cici");
        arrayList.remove("xixi");
        System.out.println(arrayList);//[lili, cici]
    }
}

LinkedList 非线程安全的 内部为双向链表

非线程安全的

 public boolean add(E e) {
        linkLast(e);
        return true;
    }
    /**
     * Links e as last element.
     */
    void linkLast(E e) {
        final Node<E> l = last;
        final Node<E> newNode = new Node<>(l, e, null);
        last = newNode;
        if (l == null)
            first = newNode;
        else
            l.next = newNode;
        size++;
        modCount++;
    }

 public boolean remove(Object o)

双链表结构

 private static class Node<E> {
        E item;
        Node<E> next;
        Node<E> prev;

        Node(Node<E> prev, E element, Node<E> next) {
            this.item = element;
            this.next = next;
            this.prev = prev;
        }
    }

新增方法

1 public boolean add(E e) {
        linkLast(e);
        return true;
    }
2 public boolean offer(E e) {
        return add(e);
    }
3 public void push(E e) {
        addFirst(e);
    }

获取第一个元素

public E peek() {
        final Node<E> f = first;
        return (f == null) ? null : f.item;
    }

获取第一个元素并删除

public E poll() {
        final Node<E> f = first;
        return (f == null) ? null : unlinkFirst(f);
    }

示例

public class T19 {
    public static void main(String[] args) {
        LinkedList linkedList=new LinkedList();
        linkedList.add("xixi");//[xixi]
        linkedList.offer("lili");//[xixi,lili]
        linkedList.push("cici");//[cici,xixi,lili]
        linkedList.remove("xixi");//[cici,lili]
        linkedList.peek();//cici [cici,lili]
        linkedList.poll();//cici [lili]
        System.out.println(linkedList);//[lili]

    }
}