Builder设计模式

GOF Builder 设计模式

Car.java

public class Car {
    private String engine;

    private String transmission;

    private String chassis;

    public String getEngine() {
        return engine;
    }

    public void setEngine(String engine) {
        this.engine = engine;
    }

    public String getTransmission() {
        return transmission;
    }

    public void setTransmission(String transmission) {
        this.transmission = transmission;
    }

    public String getChassis() {
        return chassis;
    }

    public void setChassis(String chassis) {
        this.chassis = chassis;
    }

    @Override
    public String toString() {
        return "Car{" +
                "engine='" + engine + '\'' +
                ", transmission='" + transmission + '\'' +
                ", chassis='" + chassis + '\'' +
                '}';
    }
}

　　

Builder.java

public abstract class Builder {
    public abstract void builderEngine(String engine);

    public abstract void builderTransmission(String transmission);

    public abstract void builderChassis(String chassis);

    public abstract Car build();
}

　　

CarBuilder.java

public class CarBuilder extends Builder {
    private Car car = new Car();

    @Override
    public void builderEngine(String engine) {
        car.setEngine(engine);
    }

    @Override
    public void builderTransmission(String transmission) {
        car.setTransmission(transmission);
    }

    @Override
    public void builderChassis(String chassis) {
        car.setChassis(chassis);
    }

    @Override
    public Car build() {
        return car;
    }
}

　　

Director.java

public class Director {
    private Builder builder = null;

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

    public Car createCar(String engine, String transmission, String chassis) {
        builder.builderEngine(engine);
        builder.builderTransmission(transmission);
        builder.builderChassis(chassis);
        return builder.build();
    }

    public static void main(String[] args) {
        Builder builder = new CarBuilder();
        Car car = new Director(builder).createCar("engine", "transmission", "chassis");
        System.out.println(car);
    }
}

　　

Builder设计模式变种--Java多参数问题

JavaBean多参数创建Bean时,有三种方式,创建多个构造器,使用set()/get(),使用Builder.

使用构造器: 当参数很多时,bean中需要定义很多构造器,而且对于相同类型的参数,传参顺序可能会出错,虽然可以归类参数(Effectice Java第二章有讲解),但是构造器仍然会很多

使用set/get:步骤繁多,每个参数都需要set

使用Builder:支持Fluent Interface,可以方便的创建实例

public class Person {
    private int id;
    private String name;
    private String sex;
    private String friend;

    private Person() {
    }

    private Person(Builder builder) {
        this.id = builder.id;
        this.name = builder.name;
        this.sex = builder.sex;
        this.friend = builder.friend;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getSex() {
        return sex;
    }

    public String getFriend() {
        return friend;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", friend=" + friend +
                '}';
    }

    public static class Builder {
        private int id;
        private String name;
        private String sex;
        private String friend;

        public Builder withId(int id) {
            this.id = id;
            return this;
        }

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

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

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

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

    public static void main(String[] args) {
        Person newP = new Person.Builder().withId(999).withName("hahaha").withSex("girl").withFriend("gou").build();
        System.out.println(newP);

        Person p = new Person.Builder().build();
        System.out.println(p);
    }
}