JAVA集合类测试、原理以及多线程测试比较

arrayList分析：

public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable

实现了泛型

RandomAccess是一个标记接口，接口内没有定义任何内容。

通过实现 java.io.Serializable 接口以启用其序列化功能。

private transient Object[] elementData;

private int size;

elementData:是元素，size为大小

transient:JAVA关键字，用transient声明的域，不会被Serializable序列化。

 

    public boolean add(E e) {

        ensureCapacityInternal(size + 1);  // Increments modCount!!

        elementData[size++] = e;

        return true;

    }

这个关键在于ensureCapacityInternal方法，方法代码如下，保证超过当前容量再进行扩容：

    private void ensureCapacityInternal(int minCapacity) {

        modCount++;

        // overflow-conscious code

        if (minCapacity - elementData.length > 0)

            grow(minCapacity);

    }

============================================================================================================

多线程测试：

public class ArrayListTest{

 

    public static void main(String args[]) throws InterruptedException {  

       

        //List<String> v = new ArrayList<String>();  

        List<String> v = (List<String>) Collections.synchronizedList(new ArrayList<String>());

        Thread4Collection hello1 = new Thread4Collection("hello1", v);  

        Thread4Collection hello2 = new Thread4Collection("hello2", v);  

        Thread4Collection hello3 = new Thread4Collection("hello3", v);  

 

        Thread h1 = new Thread(hello1);  

        Thread h2 = new Thread(hello2);  

        Thread h3 = new Thread(hello3);  

        h1.start();  

        h2.start();  

        h3.start();  

    }  

 

}

 

public class Thread4Collection extends Thread{

    String name;  

    List<String> v;  

    int a = 5;

    public Thread4Collection(String name, List<String> v) {

        this.name = name;

        this.v = v;

    } 

 

    public void run() {

        this.test();

    }

   

    public void test(){

        System.out.println(name + "start");

        while (a <10) {

            v.add(name + ".add");

            System.out.println(name + " list size is " + v.size());

            System.out.println(name + " list is " + v);

            try {

                Thread.sleep(10);

            } catch (InterruptedException e) {

                System.out.println(e.getMessage());

            }

            a++;

        }

 

    }

}

       

 

List<String> v = (List<String>) Collections.synchronizedList(new ArrayList<String>());

可以使arrayList实现同步，保证线程安全

 

System类arrayCopy方法测试

public static void main(String[] args) {

        //System.console();

        int[] ids = { 1, 2, 3, 4, 5 };

        System.out.println(Arrays.toString(ids));

        //测试自我复制

        //把从索引0开始的2个数字复制到索引为3的位置上

        System.arraycopy(ids, 0, ids, 3, 2);

        System.out.println(Arrays.toString(ids)); // [1, 2, 3, 1, 2]

        //复制到另一个数组中

        int[] ids2 = new int[ids.length];

        System.arraycopy(ids, 0, ids2, 0, ids.length);

        System.out.println(Arrays.toString(ids2));

    }