采取构建器(Builder)

采用构建器(Builder)
遇到多个构造器参数时, 要考虑采用构建器(Builder)
Java代码 
public A 
    private int a; 
    private int b; 
    private int c; 
    private int d; 
    public static class Builder{ 
        // 必须的 
        private final int a; 
        private final int b; 
 
        private int c; 
        private int d; 
 
        public Builder(int a, int b){ 
            this.a=a; 
            this.b=b; 
        } 
 
        public Builder setC(int c){ 
            this.c = c; 
            return this; 
        } 
 
        public Builder setD(int d){ 
            this.d=d; 
            return this; 
        } 
 
        public A build(){ 
            return new A(this); 
        } 
 
        private A(Builder builder){ 
            a = builder.a; 
            b = builder.b; 
            c = builder.c; 
            d = builder.d; 
        } 
    } 
    使用: 
    A a = new A.Builder(1, 2).setC(3).setD(4).build(); 


如果类的构造器或者静态工厂中具有多个参数, 设计这种类时, Builder模式就是一种不错的选择. 特别是大多数参数都是可选的时候. 与使用传统的重载构造器模式相比, 使用Builder模式的客户端将更易于阅读和编写.