饿汉单例模式示例

public class SingleInstance {
    /*
        饿汉单例模式：在用类创建对象的时候，对象就已经准备好了
            1.定义一个类，把构造器私有
            2.定义一个静态变量存储一个对象
     */
    public static SingleInstance instance = new SingleInstance();
    private SingleInstance(){}

    public static void main(String[] args) {
        SingleInstance instance1 = SingleInstance.instance;
        SingleInstance instance2 = SingleInstance.instance;
        SingleInstance instance3 = SingleInstance.instance;

        System.out.println(instance1);
        System.out.println(instance2);
        System.out.println(instance3);
        System.out.println(instance1 == instance3);
    }
}