单例模式

package com.singleton;

public class SingletonHungry {

    private static SingletonHungry singletonHungry = new SingletonHungry();
    
    private SingletonHungry() {}
    
    public static SingletonHungry getInstance() {
        
        return singletonHungry;
    }
    
    
    
    
    
}

package com.singleton;

public class SingletonLazy {
    
    private static SingletonLazy singletonLazy;
    
    private SingletonLazy() {}
    
    
    public synchronized static SingletonLazy getInstance() {
        
        if(singletonLazy == null) {
            
            singletonLazy = new SingletonLazy();
        }
        
        return singletonLazy;
        
    }

}

package com.singleton;

public class Test {
    
    public static void main(String[] args) {
        
        SingletonHungry singletonHungry1 = SingletonHungry.getInstance();
        SingletonHungry singletonHungry2 = SingletonHungry.getInstance();
        
        System.out.println(singletonHungry1 == singletonHungry2);
        
        
        SingletonLazy singletonLazy1 = SingletonLazy.getInstance();
        SingletonLazy singletonLazy2 = SingletonLazy.getInstance();
        
        System.out.println(singletonLazy1 == singletonLazy2);
        
    }

}