设计模式之建造者模式

形式一

建造者模式：将一个复杂对象的构建和它的表示分离，使得同样的构建过程可以创建不同的表示。即用一个抽象类规定各种建造条件，再用另一个类规定建造流程。

产品类：假设产品由多种部件组成，提供一个方法用来添加组件

public class Product {    private List<String> parts = new ArrayList<>();    public void addPart(String part) {        parts.add(part);    }    public void show() {        StringBuilder stringBuilder = new StringBuilder();        for (String part : parts) {            stringBuilder.append(part).append(",");        }        if (stringBuilder.length() > 0) {            stringBuilder.deleteCharAt(stringBuilder.length() - 1);        }        System.out.println(stringBuilder.toString());    }}

建造者接口：定义具体构建所需组件

public interface Builder {    void addPartA();    void addPartB();    void addPartC();    Product getProduct();}

具体建造者：具体实现可以调用产品类的添加方法

public class ConcreteBuilderA implements Builder {    private Product product = new Product();    @Override    public void addPartA() {        product.addPart("Part A of Product A");    }    @Override    public void addPartB() {        product.addPart("Part B of Product A");    }    @Override    public void addPartC() {        product.addPart("Part C of Product A");    }    @Override    public Product getProduct() {        return product;    }}public class ConcreteBuilderB implements Builder {    private Product product = new Product();    @Override    public void addPartA() {        product.addPart("Part A of Product B");    }    @Override    public void addPartB() {        product.addPart("Part B of Product B");    }    @Override    public void addPartC() {        product.addPart("Part C of Product B");    }    @Override    public Product getProduct() {        return product;    }}

指挥者类：定义建造具体流程

public class Director {    public Product build(Builder builder) {        builder.addPartA();        builder.addPartB();        builder.addPartC();        return builder.getProduct();    }}

测试类：

public class Test {    public static void main(String[] args) {        ConcreteBuilderA concreteBuilderA = new ConcreteBuilderA();        ConcreteBuilderB concreteBuilderB = new ConcreteBuilderB();        Director director = new Director();        Product productA = director.build(concreteBuilderA);        Product productB = director.build(concreteBuilderB);        productA.show();        productB.show();    }}

输出：

Part A of Product A,Part B of Product A,Part C of Product APart A of Product B,Part B of Product B,Part C of Product B

形式二

还有另外一种形式的建造者模式，类似于装饰者模式，只不过装饰者模式每次添加新功能都会创建新对象，这种形式的建造者模式是在原对象的基础上添加组件或者功能，典型例子是Android中的NotificationBuilder。