Builder建造者设计模式秒懂

1. 秒懂：当一个类的构造函数参数超过4个，而且这些参数有些是可选的时使用。

2. 熟悉的代码：

   Computer computer=new Computer.Builder("因特尔","三星")
   .setDisplay("三星24寸")
   .setKeyboard("罗技")
   .setUsbCount(2)
   .build();
   完美！
   

3. 实现

   public class Computer {
       private final String cpu;//必须
       private final String ram;//必须
       private final int usbCount;//可选
       private final String keyboard;//可选
       private final String display;//可选
   
       private Computer(Builder builder){
           this.cpu=builder.cpu;
           this.ram=builder.ram;
           this.usbCount=builder.usbCount;
           this.keyboard=builder.keyboard;
           this.display=builder.display;
       }
       public static class Builder{
           private String cpu;//必须
           private String ram;//必须
           private int usbCount;//可选
           private String keyboard;//可选
           private String display;//可选
   
           public Builder(String cup,String ram){
               this.cpu=cup;
               this.ram=ram;
           }
   
           public Builder setUsbCount(int usbCount) {
               this.usbCount = usbCount;
               return this;
           }
           public Builder setKeyboard(String keyboard) {
               this.keyboard = keyboard;
               return this;
           }
           public Builder setDisplay(String display) {
               this.display = display;
               return this;
           }        
           public Computer build(){
               return new Computer(this);
           }
       }
     //省略getter方法
   }