构造器优化需要多个构造器的类(建造者模式)

package com.wjy.effective;



public class BuilderConstr {
    private  final int age;
    private  final int num;
    private  final int size;
    
    public int getAge() {
        return age;
    }

    public int getNum() {
        return num;
    }

    public int getSize() {
        return size;
    }

    public static class Builder{
        private final int age;
        private final int num;
        
        private int size=0;
        
        public Builder(int age,int num){
            this.age=age;
            this.num=num;
        }
        
        public Builder size(int size){
            this.size=size;
            return this;
        }
        
        public BuilderConstr build(){
            return new BuilderConstr(this);
        }
    }
    
    public BuilderConstr(Builder builder){
        age=builder.age;
        num=builder.num;
        size=builder.size;
    }
}

客户端代码：

package com.wjy.effective;

import com.wjy.effective.BuilderConstr.Builder;

/**
 * @author wjy
 *
 */
public class TestBuildConstr {
    public static void main(String args[]){
        BuilderConstr builderConstr=new BuilderConstr.Builder(23, 1).size(88).build();
        
        //以上代码等价于以下三行代码代码：
//        Builder builder=new BuilderConstr.Builder(23, 1);
//        builder=builder.size(88);
//        BuilderConstr builderConstr=builder.build();
        
        
        
        System.out.println("age: "+builderConstr.getAge());
        System.out.println("num: "+builderConstr.getNum());
        System.out.println("size: "+builderConstr.getSize());
    }
}

运行结果：

age: 23
num: 1
size: 88