构建者模式常规写法

背景

当构建一个对象，参数超过了4个；或者构建对象，属性设置有先后顺序或依赖关系等场景，可以选择使用构建者模式

常规写法

/**
 * @Description 构造器模式
 * @Date 2021/7/22 10:49 PM
 * @Created by dwb
 * 微信: snail_java
 */
public class Computer {

    /**
     * 主板  这些属性 不需要设置 set 方法；如果需要对外提供属性，可设置get方法
     */
    private String mainBoard;

    /**
     * cpu
     */
    private String cpu;

    /**
     * 内存
     */
    private String ram;

    /**
     * 显示器
     */
    private String monitor;

    /**
     * 键盘
     */
    private String keyboard;

    /**
     * 鼠标
     */
    private String mouse;

    public static class Builder {

        private String mainBoard;
        private String cpu;
        private String ram;
        private String monitor;
        private String keyboard;
        private String mouse;

        /**
         * 必须有主板才能谈得上组装电脑；所以主板是Build构造必须条件
         *
         * @param mainBoard 鼠标
         */
        public Builder(String mainBoard) {
            this.mainBoard = mainBoard;
        }

        public Builder cpu(String cpu) {
            this.cpu = cpu;
            return this;
        }

        public Builder ram(String ram) {
            this.ram = ram;
            return this;
        }

        public Builder monitor(String monitor) {
            this.monitor = monitor;
            return this;
        }

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

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

        /**
         * 前面是组装过程；这一步才是 交付给用户的 电脑；用户可以使用该电脑
         *
         * @return 返回电脑实例
         */
        public Computer build() {
            return new Computer(this);
        }
    }

    /**
     * 注意 权限是 private；这样创建实例就交给了 Builder
     *
     * @param builder 构建者(组装电脑的人)
     */
    private Computer(Builder builder) {
        this.mainBoard = builder.mainBoard;
        this.cpu = builder.cpu;
        this.ram = builder.ram;
        this.monitor = builder.monitor;
        this.keyboard = builder.keyboard;
        this.mouse = builder.mouse;
    }

    public void start() {
        System.out.println(mainBoard + " 启动；\n"
                + ram + " 读取程序；\n"
                + cpu + " 调度程序；\n"
                + monitor + " 显示图像；\n"
                + keyboard + " 打字；\n"
                + mouse + " 控制光标");
    }

    public static void main(String[] args) {
        Computer computer = new Builder("华硕主板")
                .cpu("i5处理器").ram("金士顿内存")
                .monitor("小米显示器").keyboard("罗技键盘").mouse("雷蛇鼠标")
                .build();

        computer.start();
    }

}