一，java中的 Builder模式

• 概念
  构建者模式将客户端与包含多个组成部分(或部件)的复杂对象的创建过程分离

• 使用场景
  当构造一个对象需要很多参数的时候，并且参数的个数和类型不固定的时候

• UML结构图分析
  

  image.png
  总结：
  1.Builder：为创建产品Product对象的各个部件指定抽象接口
  2.ConcreateBuilder：实现Builder接口，实现各部件结构的构造和装配方法
  3.Product：它是被构建的复杂对象，包含多个组成部件
  4.Directior:指挥者，负责安排负责对象的建造次序，指挥者与抽象Builder之间存在关联关系

• 实际代码分析

public class Product  {
    private String partA;
    private String partB;
    private String partC;

    public String getPartA() {
        return partA;
    }

    public void setPartA(String partA) {
        this.partA = partA;
    }

    public String getPartB() {
        return partB;
    }

    public void setPartB(String partB) {
        this.partB = partB;
    }

    public String getPartC() {
        return partC;
    }

    public void setPartC(String partC) {
        this.partC = partC;
    }
}

public abstract class Builder {
    protected Product product = new Product();

    public abstract void buildPartA();

    public abstract void buildPartB();

    public abstract void buildPartC();

    public Product getResult() {
        return product;
    }
}

public class ConcreateBuilder extends Builder{


    @Override
    public void buildPartA() {

    }

    @Override
    public void buildPartB() {

    }

    @Override
    public void buildPartC() {

    }
}

public class Director {
    private Builder builder;

    public Director(Builder builder) {
        this.builder = builder;
    }

    public void setBuilder(Builder builder) {
        this.builder = builder;
    }

    public Product construct() {
        builder.buildPartA();
        builder.buildPartB();
        builder.buildPartC();
        return builder.getResult();
    }
}

 Builder builder = new ConcreateBuilder();
        Director director = new Director(builder);
        Product product = director.construct();

• 优点
  松散耦合
  容易修改内部属性
  更好的复用性(具体实现以及算法都可以复用)
• 缺点
  产生多余的Builder对象以及Dirctor对象，消耗内存
  对于构造过程的暴露

二，Builder模式在android中的应用

android中的简单实现

public class AndroidProduct {
    private String partA;
    private String partB;
    private String partC;

    private AndroidProduct(String partA, String partB, String partC) {
        this.partA = partA;
        this.partB = partB;
        this.partC = partC;
    }

    public  static class Builder {
        private String partA;
        private String partB;
        private String partC;

        public Builder setPartA(String partA) {
            this.partA = partA;
            return this;
        }

        public Builder setPartB(String partB) {
            this.partB = partB;
            return this;
        }

        public Builder setPartC(String partC) {
            this.partC = partC;
            return this;
        }

        public AndroidProduct build() {
            return new AndroidProduct(partA, partB, partC);
        }
    }
}

 AndroidProduct androidProduct = new AndroidProduct.Builder()
.setPartA("a")
.setPartB("b")
.setPartC("c").build();
   

Android中的实际应用：
1.AlertDialog
2.Gilde/okhttp