Java泛型方法定义及泛型类型推断

泛型的推断

 @Test public void test3(){ //类型推断时使用两个类型的最小公倍数 int x1 = add(3,4); Number x2 = add(3.5,4); Object obj = add(3,"abc"); } //在返回类型前加上<T> public <T> T add(T x,T y){ return x; }
  

 

  
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传入一个数组，交换其中的两项：

 @Test public void test4(){ String[] result = swap(new String[]{"abc","xyz","999"}, 1, 2); for(String s:result){ System.out.println(s); } Book[] bs = swap(new Book[]{new Book("三国演义","罗贯中"),new Book("水浒传","施耐庵"),new Book("红楼梦","曹雪芹")}, 0, 2); for(Book b:bs){ System.out.println(b.getName()+","+b.getAuthor()); } //以下做法错误,T不可以为基本类型 //int[] arr = swap(new int[]{1,2,3},1,2); } //在返回类型前加上<T> public <T> T[] swap(T[] a,int i,int j){ T temp = a[i]; a[i] = a[j]; a[j] = temp; return a; }
  

 

  
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定义泛型时限定类型：

 @Test public void test4(){ String[] result = swap(new String[]{"abc","xyz","999"}, 1, 2); for(String s:result){ System.out.println(s); } Book[] bs = swap(new Book[]{new Book("三国演义","罗贯中"),new Book("水浒传","施耐庵"),new Book("红楼梦","曹雪芹")}, 0, 2); for(Book b:bs){ System.out.println(b.getName()+","+b.getAuthor()); } //以下做法错误,T不可以为基本类型 //int[] arr = swap(new int[]{1,2,3},1,2); } //在返回类型前加上<T> public <T extends Object> T[] swap(T[] a,int i,int j){ T temp = a[i]; a[i] = a[j]; a[j] = temp; return a; }
  

 

  
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上面代码要求T要是Object的子类，这其实是废话，如果把Object改为Number则编译时上面的两个方法都会报错，因为String和Book类都不是Number的子类。

文章来源: wangsong.blog.csdn.net，作者：_江南一点雨，版权归原作者所有，如需转载，请联系作者。

原文链接：wangsong.blog.csdn.net/article/details/45400169