package demo;
/**
 * Created by sunyifeng on 17/10/19.
 */
public class MyObject {
    // 內部類
private static class MyObjectHandler{
        private static MyObject myObject = new MyObject();
};
    public MyObject() {
        // do noting
}

    public static MyObject getInstance() {
        return MyObjectHandler.myObject
 
;
}
}

package demo;
/**
 * Created by sunyifeng on 17/10/19.
 */
public class MyThread extends Thread {
    @Override
public void run() {
        super.run();
System.out.println(MyObject.getInstance());
}
}

package demo;
/**
 * Created by sunyifeng on 17/10/19.
 */
public class Run {
    public static void 
 
main(String[] args) {
        MyThread thread1 = new MyThread();
MyThread thread2 = new MyThread();
MyThread thread3 = new MyThread();
thread1.start();
thread2.start();
thread3.start();
}
}

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程式分析：

1、定義一個靜態內部類，在裡面建立例項；通過靜態的getInstance()方法返回單例。

2、多個執行緒取到的是同一例項。