单例设计模式

package p1;

//饿汉设计模式
//由于饿，开始就创建实例
public class TestSingleton1 {

    public static void main(String[] args) {
        Singletion s1 = Singletion.getSingletion();
        Singletion s2 = Singletion.getSingletion();
        System.out.println(s1 == s2);

    }

}

class Singletion {
    // 1.私有化构造器，使外部类不能调用此构造器
    private Singletion() {

    }

    // 2.在该类中创建一个类的实例，私有化该对象，通过公共方法调用
    private static Singletion instance = new Singletion();

    // 3.定义一个公共的static方法
    public static Singletion getSingletion() {
        return instance;
    }
}

package p1;

//懒汉模式: 可能存在线程安全问题
//由于懒，先不创建实例，等比较之后，再创建
public class TestSingleton2 {

    public static void main(String[] args) {
        Singletion s1 = Singletion.getSingletion();
        Singletion s2 = Singletion.getSingletion();
        System.out.println(s1 == s2);
    }
}

class Singleton {
    private Singleton() {

    }

    private static Singleton instance = null;

    public static Singleton getSingleton() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}