泛型讨论------一个元组类库

仅一个方法调用就能返回多个对象，我们应该经常有这样的需求，可是return语句只允许返回单个对象。因此，解决的办法就是创意一个对象。

就是我要说的元组，即：将一组对象直接打包存储与其中的一个单一对象，一个容器对象允许读取其中元素，但是不允许向其中存放新的对象。

 

看例子说问题:

 

 

public class TwoTuple<A,B>{

	public final A first;
	public final B second;
	
	public TwoTuple(A a,B b){
		first = a;
		second = b;
	}

	public String toString(){
		return "("+first+" .."+second+")";
	}
}

 

 

 

我们可以使用继承机制实现长度更长的元组，办法就是增加类型参数

 

 

public class ThreeTuple<A,B,C> extends TwoTuple<A,B> {
  public final C third;
  public ThreeTuple(A a, B b, C c) {
    super(a, b);
    third = c;
  }
  public String toString() {
    return "(" + first + ", " + second + ", " + third +")";
  }
} 

 

 

public class FourTuple<A,B,C,D> extends ThreeTuple<A,B,C> {
  public final D fourth;
  public FourTuple(A a, B b, C c, D d) {
    super(a, b, c);
    fourth = d;
  }
  public String toString() {
    return "(" + first + ", " + second + ", " +
      third + ", " + fourth + ")";
  }
}

 

 

 

public class FiveTuple<A,B,C,D,E>
extends FourTuple<A,B,C,D> {
  public final E fifth;
  public FiveTuple(A a, B b, C c, D d, E e) {
    super(a, b, c, d);
    fifth = e;
  }
  public String toString() {
    return "(" + first + ", " + second + ", " +
      third + ", " + fourth + ", " + fifth + ")";
  }
} 

 

 

为了使用元组，我们只需定义一个长度合适的元组，将其作为方法的返回值，然后再return语句中创建该元组，然后返回即可。

 

看下来的例子，很经典，值得收藏

 

public class Tuple {
  public static <A,B> TwoTuple<A,B> tuple(A a, B b) {
    return new TwoTuple<A,B>(a, b);
  }
  public static <A,B,C> ThreeTuple<A,B,C>
  tuple(A a, B b, C c) {
    return new ThreeTuple<A,B,C>(a, b, c);
  }
  public static <A,B,C,D> FourTuple<A,B,C,D>
  tuple(A a, B b, C c, D d) {
    return new FourTuple<A,B,C,D>(a, b, c, d);
  }
  public static <A,B,C,D,E>
  FiveTuple<A,B,C,D,E> tuple(A a, B b, C c, D d, E e) {
    return new FiveTuple<A,B,C,D,E>(a, b, c, d, e);
  }
}

 

由于有了泛型，你可以很容易的创意元组，只是编写表达式而已！