构建者模式（Builder）

定义

将一个复杂对象的构建与其表示分离，使得同样的构建过程可以创建不同的表示

使用场景

主要角色

1. 产品 Product
2. 建造者接口 Builder
3. 具体的建造者 Concrete Builder
4. 指挥者 Director:组织构建过程

示例代码

@Data
public class Computer {
    private String cpu;//必须
    private String ram;//必须
    private int usbCount;//可选
    private String keyboard;//可选
    private String display;//可选

    public Computer(String cpu, String ram) {
        this.cpu = cpu;
        this.ram = ram;
    }

}

public abstract class ComputerBuilder {
    public abstract void setUsbCount();
    public abstract void setKeyboard();
    public abstract void setDisplay();

    public abstract Computer build();
}

public class LenovoComputerBuilder extends ComputerBuilder {
    private Computer computer;
    public LenovoComputerBuilder(String cpu, String ram) {
        computer=new Computer(cpu,ram);
    }
    @Override
    public void setUsbCount() {
        computer.setUsbCount(4);
    }
    @Override
    public void setKeyboard() {
        computer.setKeyboard("联想键盘");
    }
    @Override
    public void setDisplay() {
        computer.setDisplay("联想显示器");
    }
    @Override
    public Computer build() {
        return computer;
    }
}

public class MacComputerBuilder extends ComputerBuilder {
    private Computer computer;
    public MacComputerBuilder(String cpu, String ram) {
        computer = new Computer(cpu, ram);
    }
    @Override
    public void setUsbCount() {
        computer.setUsbCount(2);
    }
    @Override
    public void setKeyboard() {
        computer.setKeyboard("苹果键盘");
    }
    @Override
    public void setDisplay() {
        computer.setDisplay("苹果显示器");
    }
    @Override
    public Computer build() {
        return computer;
    }
}

public class ComputerDirector {
    public void makeComputer(ComputerBuilder builder){
        builder.setUsbCount();
        builder.setDisplay();
        builder.setKeyboard();
    }
}

public class Client {
    public static void main(String[] args) {
        ComputerDirector director = new ComputerDirector();
        ComputerBuilder builder = new MacComputerBuilder("I5处理器", "三星125");
        director.makeComputer(builder);
        Computer macComputer = builder.build();
        System.out.println("mac computer:" + macComputer.toString());

        ComputerBuilder lenovoBuilder = new LenovoComputerBuilder("I7处理器", "海力士222");
        director.makeComputer(lenovoBuilder);
        Computer lenovoComputer = lenovoBuilder.build();
        System.out.println("lenovo computer:" + lenovoComputer.toString());
    }
}

mac computer:Computer(cpu=I5处理器, ram=三星125, usbCount=2, keyboard=苹果键盘, display=苹果显示器)
lenovo computer:Computer(cpu=I7处理器, ram=海力士222, usbCount=4, keyboard=联想键盘, display=联想显示器)