GOF—建造者模式

将一个复杂对象的构建与表示分离，使得同样的构建过程可以创建不同的表示。

1. 抽象建造者：规定要实现复杂对象的那些部分创建，并不涉及具体的部件对象的创建。
2. 具体建造者：实现抽象建造者，完成复杂产品的各个部件的具体创建方法，在构造过程完成后，提供产品的实例。
3. 产品类：要创建的复杂对象。
4. 指挥者：调用具体建造者来创建复杂对象的各个部分，在指挥者中不涉及具体产品的信息，只复杂保证对象各部分完整创建或按某种顺序创建。 抽象建造者

// 抽象 builder 类
public abstract class Builder {

    protected Bike mBike = new Bike();

    public abstract void buildFrame();
    public abstract void buildSeat();
    public abstract Bike createBike();
}

具体建造者(摩拜)

//摩拜单车Builder类
public class MobikeBuilder extends Builder {

    @Override
    public void buildFrame() {
        mBike.setFrame("铝合金车架");
    }

    @Override
    public void buildSeat() {
        mBike.setSeat("真皮车座");
    }

    @Override
    public Bike createBike() {
        return mBike;
    }
}

具体建造者(Ofo)

//ofo单车Builder类
public class OfoBuilder extends Builder {

    @Override
    public void buildFrame() {
        mBike.setFrame("碳纤维车架");
    }

    @Override
    public void buildSeat() {
        mBike.setSeat("橡胶车座");
    }

    @Override
    public Bike createBike() {
        return mBike;
    }
}

产品类(自行车)

//自行车类
public class Bike {
    private String frame;
    private String seat;

    public String getFrame() {
        return frame;
    }

    public void setFrame(String frame) {
        this.frame = frame;
    }

    public String getSeat() {
        return seat;
    }

    public void setSeat(String seat) {
        this.seat = seat;
    }
}

指挥者

//指挥者类
public class Director {
    private Builder mBuilder;

    public Director(Builder builder) {
        mBuilder = builder;
    }

    public Bike construct() {
        mBuilder.buildFrame();
        mBuilder.buildSeat();
        return mBuilder.createBike();
    }
}

测试类

//测试类
public class Client {
    public static void main(String[] args) {
        showBike(new OfoBuilder());
        showBike(new MobikeBuilder());
    }
    private static void showBike(Builder builder) {
        Director director = new Director(builder);
        Bike bike = director.construct();
        System.out.println(bike.getFrame());
        System.out.println(bike.getSeat());
    }
}

但是有些情况下需要简化系统结构，可以把指挥者类和抽象建造者进行结合

// 抽象 builder 类
public abstract class Builder {

    protected Bike mBike = new Bike();

    public abstract void buildFrame();
    public abstract void buildSeat();
    public abstract Bike createBike();
    
    public Bike construct() {
        this.buildFrame();
        this.BuildSeat();
        return this.createBike();
    }
}

模式扩展

public class Phone {

    private String cpu;
    private String screen;
    private String memory;
    private String mainboard;

    private Phone(Builder builder) {
        cpu = builder.cpu;
        screen = builder.screen;
        memory = builder.memory;
        mainboard = builder.mainboard;
    }
    // 静态方式调用
    public static Builder builder(){
        return new Builder();
    }

    public static final class Builder {
        private String cpu;
        private String screen;
        private String memory;
        private String mainboard;

        public Builder() {}

        public Builder cpu(String val) {
            cpu = val;
            return this;
        }
        public Builder screen(String val) {
            screen = val;
            return this;
        }
        public Builder memory(String val) {
            memory = val;
            return this;
        }
        public Builder mainboard(String val) {
            mainboard = val;
            return this;
        }
        public Phone build() {
            return new Phone(this);}
    }
    @Override
    public String toString() {
        return "Phone{" +
                "cpu='" + cpu + '\'' +
                ", screen='" + screen + '\'' +
                ", memory='" + memory + '\'' +
                ", mainboard='" + mainboard + '\'' +
                '}';
    }
}

public class Client {
    public static void main(String[] args) {
        // 返回this对象，进行链式编程
        Phone phone = new Phone.Builder()
                .cpu("intel")
                .mainboard("华硕")
                .memory("金士顿")
                .screen("三星")
                .build();
        System.out.println(phone);
        
        phone = Phone.builder()
                .cpu("intel")
                .mainboard("华硕")
                .memory("三星")
                .screen("三星")
                .build()；
       System.out.println(phone);
    }
}