一文详解Java的饿汉和懒汉设计模式

public class HungerModel {
    public static void main(String[] args) {
//        GirlFriend girlFriend1 = new GirlFriend("white", 34);
//        GirlFriend girlFriend2 = new GirlFriend("jack", 20);
//        System.out.println(girlFriend1);
//        System.out.println(girlFriend2);
        GirlFriend girlFriend1 = GirlFriend.getInstance();
        System.out.println(girlFriend1);

        GirlFriend girlFriend2 = GirlFriend.getInstance();
        System.out.println(girlFriend2);

        System.out.println(girlFriend1 == girlFriend2);

    }

}

// 只能有一个女朋友,即只能创建一个girlfriend对象?

class GirlFriend {
    private String name;
    private int age;
    private static GirlFriend girl = new GirlFriend("布尔玛",20);

    /**
     * (1) 将构造器私有化，不允许其他类调用该构造器
     * (2) 类中创建该对象实例，私有化，设置为静态，使用无需创建对象，直接用类.静态变量访问.
     * (3) 提供static公共方法，返回实例对象
     * @param name
     * @param age
     */

    public static GirlFriend getInstance(){
        return girl;
    }

    private GirlFriend(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "GirlFriend{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

public class LazyModel {
    public static void main(String[] args) {
        GirlFriend_ girlFriend1 = GirlFriend_.getInstance();
        System.out.println(girlFriend1);

        GirlFriend_ girlFriend2 = GirlFriend_.getInstance();
        System.out.println(girlFriend2);

        System.out.println(girlFriend1 == girlFriend2);
    }
}
class GirlFriend_ {
    private String name;
    private int age;
    private static GirlFriend_ girlFriend ; // 默认初始值为null

    /**
     * (1) 构造器私有化
     * (2) 类成员中添加对象引用，static ,private,不要直接new,
     * (3) 提供公共方法，返回对象实例 ,public,判断当前对象是否为空，
     *      若为空，则创建，若不为空，直接返回该对象。
     * @param name
     * @param age
     */

    private GirlFriend_(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public static GirlFriend_ getInstance(){
        if(girlFriend == null){
            girlFriend = new GirlFriend_("布尔玛",20);
        }
        return girlFriend;
    }

    @Override
    public String toString() {
        return "GirlFriend_{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

public class HungerModel {
    public static void main(String[] args) {
        System.out.println(GirlFriend.id);

    }

}

// 只能有一个女朋友,即只能创建一个girlfriend对象?

class GirlFriend {
    private String name;
    private int age;
    public static int id = 1001;
    private static GirlFriend girl = new GirlFriend("布尔玛",20);

    /**
     * (1) 将构造器私有化，不允许其他类调用该构造器
     * (2) 类中创建该对象实例，私有化，设置为静态，使用无需创建对象，直接用类.静态变量访问.
     * (3) 提供static公共方法，返回实例对象
     * @param name
     * @param age
     */

    public static GirlFriend getInstance(){
        return girl;
    }

    private GirlFriend(String name, int age) {
        this.name = name;
        this.age = age;
        System.out.println("GirlFriend类的private GirlFriend(String name, int age)构造器被调用");
    }

    @Override
    public String toString() {
        return "GirlFriend{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

public class LazyModel {
    public static void main(String[] args) {
        System.out.println(GirlFriend_.id);
        System.out.println(GirlFriend_.getInstance());
    }
}
class GirlFriend_ {
    private String name;
    private int age;
    public static int id = 1002;
    private static GirlFriend_ girlFriend ; // 默认初始值为null

    /**
     * (1) 构造器私有化
     * (2) 类成员中添加对象引用，static ,private,不要直接new,
     * (3) 提供公共方法，返回对象实例 ,public,判断当前对象是否为空，
     *      若为空，则创建，若不为空，直接返回该对象。
     * @param name
     * @param age
     */

    private GirlFriend_(String name, int age) {
        this.name = name;
        this.age = age;
        System.out.println("GirlFriend_类的private GirlFriend_(String name, int age)构造器被调用");
    }

    public static GirlFriend_ getInstance(){
        if(girlFriend == null){
            girlFriend = new GirlFriend_("布尔玛",20);
        }
        return girlFriend;
    }

    @Override
    public String toString() {
        return "GirlFriend_{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}