Builder注解

● 它作用于类，将其变成建造者模式
● 可以以链的形式调用
● 初始化实例对象生成的对象是不可以变的，可以在创建对象的时候进行赋值
● 如果需要在原来的基础上修改可以加 set 方法，final 字段可以不需要初始化
● 它会生成一个全参的构造函数

实战：

@Builder
public class User {
    private String username;
    private String password;
}

编译后：

public class User {
    private String username;
    private String password;
    
    User(String username, String password) {
        this.username = username;
        this.password = password;
    }
    
    public static User.UserBuilder builder() {
        return new User.UserBuilder();
    }
	
    public static class UserBuilder {
        private String username;
        private String password;
        
        UserBuilder() {}
		
        public User.UserBuilder username(String username) {
            this.username = username;
            return this;
        }
        
        public User.UserBuilder password(String password) {
            this.password = password;
            return this;
        }
        
        public User build() {
            return new User(this.username, this.password);
        }
        
		public String toString() {
            return "User.UserBuilder(username=" + this.username + ", password=" + this.password + ")";
        }
    }
}