建造者模式

建造者模式：封装一个对象的构造过程，并允许按步骤构造。

有两种形式：传统建造者模式和传统建造者模式变种。

传统建造者模式：

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

    private Computer(Builder builder){
        this.cpu=builder.cpu;
        this.ram=builder.ram;
        this.usbCount=builder.usbCount;
        this.keyboard=builder.keyboard;
        this.display=builder.display;
    }
    public static class Builder{
        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 Builder(String cup,String ram){
            this.cpu=cup;
            this.ram=ram;
        }
        public Builder setDisplay(String display) {
            this.display = display;
            return this;
        }       
        //set...
        public Computer build(){
            return new Computer(this);
        }
    }
}

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

传统建造者模式变种，链式调用：

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 Computer getComputer() {
        return computer;
    }
}

Computer computer=new Computer.Builder("因特尔","三星")
                .setDisplay("三星24寸")
                .setKeyboard("罗技")
                .setUsbCount(2)
                .build();