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创建通用函数以复制不同的对象

copy java-8 object java

NoobEditor · 技术社区 · 6 年前

所以我有一个我需要的用例复制安 object 属于 class ES(等级可能因工厂输入类型而异。

这是我想做的事情的一个例子

public interface DataUtil {

    // the main wrapper 
    static Object copyObject(Object payload){
        if(payload instanceof Human))
            return copyEntry((Human) payload);
        if(payload instanceof Car))
            return copyEntry((Car) payload);
        if(payload instanceof Planet))
            return copyEntry((Planet) payload);        
        return payload;
    }

    static Human copyEntry(Human human) {
        return Human.builder()
                .name(human.getName())
                .age(human.getAge())
                .build();
    }

    static Car copyEntry(Car car) {
        return Car.builder()
                .model(car.getModel())
                .brand(car.getBrand())
                .build();
    }

    static Planet copyEntry(Planet planet) {
        // return builder like previous
    }
}

如果你看 copyObject 函数,它按预期执行作业,但问题属于返回类型。目前,为了使自己 兼容的 ,它返回一个 Object 但是我宁愿返回它特定的类对象(比如 Human 或 Car 例如)

有没有办法用仿制药(用 <T> )?或者这是一个糟糕的方法在第一个地方做?

3 回复 | 直到 6 年前

NoobEditor 6 年前

Object
instanceof

public interface Copyable<T> {
    T copy(T t);
}

public class Human implements Copyable<Human> {

   @Override
   public Human copy(Human t) {
       return    Human.builder()
                     .name(human.getName())
                     .age(human.getAge())
                     .build();
   }

}

// the main wrapper
static <T extends Copyable<T>> T copyObject(T payload) {
    return payload.copy(payload);
}

Human human = new Human();
// set some fields  ...
Human copiedHuman = copyObject(human); // compile
Car copiedCar = copyObject(human); // doesn't compile

copyObject() CopyVisitor

@SuppressWarnings("unchecked")
static <T extends Visited> T copyObject(T payload) {
    CopyVisitor visitor = new CopyVisitor();
    payload.accept(visitor);
    return (T) visitor.getCopy();
}

Visitor

public interface Visitor {  
    void visitHuman(Human human);
    void visitCar(Car car);
    void visitPlanet(Planet planet);
}

public class CopyVisitor implements Visitor {

    private Visited copy;

    @Override
    public void visitHuman(Human human) {
        copy = Human.builder()
                    .name(human.getName())
                    .age(human.getAge())
                    .build();

    }

    @Override
    public void visitCar(Car car) {
        copy = Car.builder()
                  .model(car.getModel())
                  .brand(car.getBrand())
                  .build();
    }

    @Override
    public void visitPlanet(Planet planet) {
        //...
    }

    public Visited getCopy() {
        return copy;
    }

}

public interface Visited {
    void accept(Visitor visitor);
}

public class Human implements Visited {

    @Override
    public void accept(Visitor visitor) {
        visitor.visitHuman(this);
    }

}

copy()

Alexander Egger 6 年前

static <TPayload> TPayload copyObject(Object payload) {
    if (payload instanceof Human)
        return (TPayload) copyEntry((Human) payload);
    if (payload instanceof Car)
        return (TPayload) copyEntry((Car) payload);
    if (payload instanceof Planet)
        return (TPayload) copyEntry((Planet) payload);
    return (TPayload) payload;
}

Number n = DataUtil.copyObject("someString");

iconfly 6 年前

static <T> T copyObject(Object payload)
    {
        if (payload instanceof Human)
        {
            return (T) copyEntry((Human) payload);
        }
        if (payload instanceof Car)
        {
            return (T) copyEntry((Car) payload);
        }
        if (payload instanceof Planet)
        {
            return (T) copyEntry((Planet) payload);
        }
        return (T) payload;
    };

Human h1 = new ...
Human h2= copyObject(h1);

List<Object>