java：单例模式

单例模式

1）饿汉式：在一开始记加载时就进行初始化

class A{
	private static A onlyOne = new A();
	private A() {/*将构造函数私有化*/}
	public static A getA() {
		return onlyOne;
	}
}

public class FirstClass {
	public static void main(String[] args) {
		A a = A.getA();
	}
}

2）懒汉式：在需要时，才进行初始化

class A{
	private static A onlyOne = null;
	private A() {//将构造函数私有化
	}
	public static A getA() {//在获取唯一实例时，查看是否已经创建该实例
		if(onlyOne == null) {
			onlyOne = new A();
		}
		return onlyOne;
	}
}

public class FirstClass {
	public static void main(String[] args) {
		A a = A.getA();
	}
}