将一个复杂的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。

我在这里以电脑组装为例

public class Computer {

    private String cpu;

    private String mainBoard;

    private String gpu;

    private String power;

    private String memory;

    private String hardDisk;

    private String radiator;

    private String box;

    /*省略get和set方法，请自行添加*/

    @Override
    public String toString() {
        return "Computer{" +
                "cpu='" + cpu + '\'' +
                ", mainBoard='" + mainBoard + '\'' +
                ", gpu='" + gpu + '\'' +
                ", power='" + power + '\'' +
                ", memory='" + memory + '\'' +
                ", hardDisk='" + hardDisk + '\'' +
                ", radiator='" + radiator + '\'' +
                ", box='" + box + '\'' +
                '}';
    }
}

public abstract class Builder {

    public Computer computer = new Computer();

    public abstract void buildCpu();

    public abstract void buildMainBoard();

    public abstract void buildGpu();

    public abstract void buildPower();

    public abstract void buildMemory();

    public abstract void buildHardDisk();

    public abstract void buildRadiator();

    public abstract void buildBox();

    public abstract Computer installComputer();
}

public class ComputerBuilder extends Builder {

    @Override
    public void buildCpu() {
        computer.setCpu("AMD R5 5800X");
    }

    @Override
    public void buildMainBoard() {
        computer.setMainBoard("msi B550 MORTAR");
    }

    @Override
    public void buildGpu() {
        computer.setGpu("RTX3060");
    }

    @Override
    public void buildPower() {
        computer.setPower("鑫谷650W");
    }

    @Override
    public void buildMemory() {
        computer.setMemory("Kingston DDR4 8GB * 4");
    }

    @Override
    public void buildHardDisk() {
        computer.setHardDisk("SAMSUNG SSD NVMe 500G m.2");

    }

    @Override
    public void buildRadiator() {
        computer.setRadiator("九州风神水冷");
    }

    @Override
    public void buildBox() {
        computer.setBox("淘宝挑个自己喜欢的");
    }

    @Override
    public Computer installComputer() {
        return computer;
    }
}

public class Installer {

    private Builder builder;

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

    public Computer assembly(){
        builder.buildCpu();
        builder.buildBox();
        builder.buildGpu();
        builder.buildHardDisk();
        builder.buildMainBoard();
        builder.buildMemory();
        builder.buildPower();
        builder.buildRadiator();
        return builder.installComputer();
    }
}

public class Client {
    public static void main(String[] args) {

        Installer installer = new Installer(new ComputerBuilder());

        Computer computer = installer.assembly();

        System.out.println(computer.toString());

    }
}

结果

Computer{cpu='AMD R5 5800X', mainBoard='msi B550 MORTAR', gpu='RTX3060', power='鑫谷650W', memory='Kingston DDR4 8GB * 4', hardDisk='SAMSUNG SSD NVMe 500G m.2', radiator='九州风神水冷', box='淘宝挑个自己喜欢的'}