单例,顾名思义就是某一个类在整个程序系统中有且仅有一个实例,称为单例。单例能被整个程序系统访问。创建单例的时候应该使用类方法创建,因为让类的实例去生成另一个唯一的实例变得毫无意义.
饿汉式
package com.hc;
public class Test {
public static void main( String[] args){
Singleton1 single1 = Singleton1.getInstance();
Singleton1 single2 = Singleton1.getInstance();
System.out.println("single1"+single1);
System.out.println("single2"+single2);
}
}
/*
static修饰的常量会在构造方法加载时加载,因此在使用到类Singleton1的时候
就会加载构造方法,同时private static Singleton1 singleton1 = new Singleton1();就实例就创建了,
并且static修饰的变量只会创建一次,在程序中只有一份内存
*/
class Singleton1 {
private static Singleton1 singleton1 = new Singleton1();
private Singleton1(){
System.out.println("构造方法");
}
public static Singleton1 getInstance(){
return singleton1;
}
}
懒汉式
package com.hc;
public class Test {
public static void main( String[] args){
Singleton1 single1 = Singleton1.getInstance();
Singleton1 single2 = Singleton1.getInstance();
System.out.println("single1"+single1);
System.out.println("single2"+single2);
}
}
class Singleton1 {
private static Singleton1 singleton1 = null;
private Singleton1(){
System.out.println("构造方法");
}
public static Singleton1 getInstance(){
if(singleton1 == null){
singleton1 = new Singleton1();
}
return singleton1;
}
}
