两种设计模式（单例，构造者）

单例模式

package com.example.demo01;

public class User {

    //设置私有静态方法 获取对象
    private static User user = new User();

    //设置私有变量
    private String name;

    //私有构造
    private User(){
    }

    //设置方法，供外界调用
    public static User getUser(){
        return user;
    }



    //主方法
    public static void main(String[] args) {
        //获取对象
        User user = User.getUser();
        User user1 = User.getUser();

        //判断是否是同一个对象
        if(user == user1){
            System.out.println("这是同一个对象");
        }

    }

}

构造者模式

package com.example.demo01;

import android.net.Uri;

public class Person {

    String name;
    int age ;
    String email;
    String address;

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

    //创建内部类
    public static class Builder{
        String name;
        int age ;
        String email;
        String address;

        //空参构造
        public Builder() {
        }

        //赋值返回
        public Builder setName(String name) {
            this.name = name;
            return this;
        }
        public Builder setEmail(String email) {
            this.email = email;
            return this;
        }
        public Builder setAddress(String address) {
            this.address = address;
            return this;
        }

        //通过build来创建一个类
        public Person build(){
            Person person = new Person();
            person.name = name;
            person.email = email;
            person.address = address;
            return person;
        }
    }

    public static void main(String[] args) {
        //调用方法来获取想要的类
        Person person = new Person.Builder().setName("张三").setEmail("123").setAddress("天国").build();
        System.out.println(person.toString());




    }




}

结果

"C:\Program Files\Android\Android Studio\jre\bin\java.exe" "-javaagent:C:\Program Files\Android\Android Studio\lib\idea_rt.jar=50372:C:\Program Files\Android\Android Studio\bin" 1.1.3.jar com.example.demo01.Person
Person{name='张三', age=0, email='123', address='天国'}