其他设计模式
java单例模式
java建造者模式
java策略模式
java代理模式
java观察者模式
java适配器模式
java外观模式

使用场景

遇到多个构造器参数时要考虑用构造器

实现

不直接生产想要的对象，而是让客户端利用所以必要的参数调用构造器，得到一个builder对象，最后，客户端调用无参的build方法来生产不可变的对象，这个bulider是它构建的类的静态成员类

public class Student {
    private final String name;
    private final int age;
    private final int height;
    private final int sex;
    private final String schoolName;
    private final String profession;


    public static class Builder {
        private final String name;
        private final int age;
        private  int height;
        private  int sex;
        private String schoolName;
        private String profession;

        public Builder(String name, int age) {
            this.name = name;
            this.age = age;
        }

        public Builder height(int val) {
            height = val;
            return this;
        }

        public Builder sex(int val) {
            sex = val;
            return this;
        }

        public Builder schoolName(String val) {
            this.schoolName = val;
            return this;
        }

        public Builder sprofession(String val) {
            profession = val;
            return this;
        }

        //        构造器入口
        public Student build() {
            return new Student(this);
        }

    }

    private Student(Builder builder) {
        this.name = builder.name;
        this.age = builder.age;
        this.height = builder.height;
        this.sex = builder.sex;
        this.schoolName = builder.schoolName;
        this.profession = builder.profession;
    }
}

注意Sutdent是不可变的，所有的默认参数值都单独放在一个地方，builder的setter方法返回builder本身，以便可以把调用链接起来，下面就是客户端代码：

Student jack=new Student.Builder("jack",20).height(173).schoolName("Harvard ").build();
Student lucy=new Student.Builder("lucy",21).height(163).sex(1).schoolName("Harvard ").build();

上述代码name和age是作为必需参数，故放在builder的构造器参数中， 如果都是可选参数，就都可以参照height，sex等参数的写法