【设计模式】java单实例模式代码示例

单实例模式是java常用的设计模式，目的是保证各个引用的都是同一个对象。

例如系统的回收站只有一个，每一个引用的地方都只用引用已经创建出来的实例。

以下是单实例模式的实现和测试代码：

 

class TestClass
{
private static TestClass instance;

private int num = 0;

public static TestClass getInstance()
{
if (null == instance)
{
instance = new TestClass();
}
return instance;
}

public int getNum()
{
return this.num;
}

public void setNum(int aNum)
{
this.num = aNum;
}
}

public class SingleInstance {

/**
* @param args
*/
public static void main(String[] args)
{
TestClass Instance_1 = TestClass.getInstance();
System.out.println("num = " + Instance_1.getNum());
Instance_1.setNum(10);
System.out.println("num = " + Instance_1.getNum());

TestClass Instance_2 = TestClass.getInstance();
System.out.println("num = " + Instance_2.getNum());
Instance_2.setNum(20);
System.out.println("num = " + Instance_2.getNum());

TestClass Instance_3 = TestClass.getInstance();
System.out.println("num = " + Instance_3.getNum());
Instance_3.setNum(30);
System.out.println("num = " + Instance_3.getNum());
}

}

控制台输出结果：

num = 0

num = 10

num = 10

num = 20

num = 20

num = 30