Java:unchecked调用compareTo(T)

Question

 1  class test {
 2      public static int compare0(Comparable x, Comparable y) {
 3          return x.compareTo(y);
 4      }

 5      public static int compare1(Object x, Object y) {
 6          return ((Comparable) x).compareTo((Comparable) y);
 7      }

 8      public static int compare2(Object x, Object y) {
 9          Comparable p = (Comparable) x;
10          Comparable q = (Comparable) y;
11          return (p).compareTo(q);
12      }

13      public static void main(String[] args) {
14          Comparable zero = new Integer(0);
15          Comparable one = new Integer(1);
16          int c = (zero).compareTo(one);
17      }
18  }

编译上面的代码会产生4个警告:

% javac -Xlint:unchecked test.java
test.java:3: warning: [unchecked] unchecked call to compareTo(T) as a member of the raw type java.lang.Comparable
    return x.compareTo(y);
                      ^
test.java:7: warning: [unchecked] unchecked call to compareTo(T) as a member of the raw type java.lang.Comparable
    return ((Comparable) x).compareTo((Comparable) y);
                                     ^
test.java:13: warning: [unchecked] unchecked call to compareTo(T) as a member of the raw type java.lang.Comparable
    return (p).compareTo(q);
                        ^
test.java:19: warning: [unchecked] unchecked call to compareTo(T) as a member of the raw type java.lang.Comparable
    int c = (zero).compareTo(one);
                            ^
4 warnings

我尝试了更多的变种,但警告仍然存在.编写和调用上面的test.compare方法的正确方法是什么？

谢谢!

PS:test.compare只是一个例子; 我不需要这样的功能; 但我需要实现一个函数,就像test.compare一样,需要在其签名中包含Comparable实现对象.

PS2:我已经编程了25年以上,我甚至在大约10年前编写了Java一段时间,但现在使用Java(我的工作需要)让我疯狂.对于有经验的程序员来说,学习Java比看起来要困难得多.在那里学习Java有很多东西,其中99%最好是过时的,或者倾向于对编程新手进行排名(即大量冗长),最糟糕的是直接垃圾...我还没有找到关于Java将让我快速回答上述问题的答案.

Answer 1

Comparable 是通用的 - 您应该使用定义变量 Comparable<Integer>

Answer 2

您应该compare使用泛型参数声明该方法.

public class ThisTest
{
    public static <T extends Comparable<T>> int compare(T x, T y) {
        if (x == null) 
            return -(y.compareTo(x));
        return x.compareTo(y);
    }

    public static void main()
    {
        // Type inferred
        int c = compare(Integer.valueOf(0), Integer.valueOf(1));
        // Explicit generic type parameter
        c = ThisTest.<Integer>compare(Integer.valueOf(0), Integer.valueOf(1));
    }
}