每天一个设计模式之Builder模式

Builder模式也是一种创建型模式，它主要适用于创建具有较多属性的对象，有些属性是可选的，有些是必选的。拿电脑攒机来举例，CPU、硬盘、内存条、主板等部件是必须具备的，而显示器、键盘、鼠标等不一定需要（比如服务器），这样的场景非常适合使用Builder模式来创建对象。

将一个复杂对象的创建与它的表示分离，使得同样的构建过程可以创建不同的表示。

1. Builder，为创建目标对象的各个部件指定抽象接口。
2. ConcreteBuilder，实现Builder接口以构造和装配产品的各个部件。
3. Product，表示一个复杂的对象。
4. Client，一个使用Builder接口的对象。

package builder;

public class Computer {
    private CPU cpu;
    private Mouse mouse;
    private HardDisk disk;
    private Keyboard keyboard;

    private Computer(Builder builder) {
        this.cpu = builder.cpu;
        this.mouse = builder.mouse;
        this.disk = builder.disk;
        this.keyboard = builder.keyboard;
    }

    @Override
    public String toString() {
        return "Computer{" +
                "cpu=" + cpu +
                ", mouse=" + mouse +
                ", disk=" + disk +
                ", keyboard=" + keyboard +
                '}';
    }

    public static class Builder {
        private CPU cpu;
        private Mouse mouse;
        private HardDisk disk;
        private Keyboard keyboard;

        public Builder(CPU cpu, HardDisk disk) {
            this.cpu = cpu;
            this.disk = disk;
        }

        public Builder addMouse(Mouse mouse) {
            this.mouse = mouse;
            return this;
        }

        public Builder addKeyboard(Keyboard keyboard) {
            this.keyboard = keyboard;
            return this;
        }

        public Computer build() {
            return new Computer(this);
        }
    }
}

package builder;

public abstract class Part {
    private String partName;

    public Part(String partName) {
        this.partName = partName;
    }

    @Override
    public String toString() {
        return "Part{" +
                "partName='" + partName + ''' +
                '}';
    }
}

class HardDisk extends Part {
    public HardDisk(String partName) {
        super(partName);
    }
}

class Keyboard extends Part {
    public Keyboard(String partName) {
        super(partName);
    }
}

class Mouse extends Part {
    public Mouse(String partName) {
        super(partName);
    }
}

class CPU extends Part {
    public CPU(String partName) {
        super(partName);
    }
}

package builder;

public class Client {
    public static void main(String[] args) {
        Computer computer = new Computer.Builder(new CPU("AMD"), new HardDisk("Sumsung"))
                .addMouse(new Mouse("Swift"))
                .addKeyboard(new Keyboard("Unknown")).build();
        System.out.println(computer.toString());
    }

}

// 打印结果
Computer{cpu=Part{partName='AMD'}, mouse=Part{partName='Swift'}, disk=Part{partName='Sumsung'}, keyboard=Part{partName='Unknown'}}

Process finished with exit code 0

1. https://www.digitalocean.com/community/tutorials/builder-design-pattern-in-java
2. https://en.wikipedia.org/wiki/Builder_pattern