有趣的Java泛型

时间:2009-09-17 10:43:06

标签: java generics comparable

有人知道如何使用泛型编写下面的代码并避免编译器警告吗? (@SuppressWarnings(“未选中”)被视为作弊)。

而且,也许,通过泛型检查“左”的类型是否与“右”的类型相同?

public void assertLessOrEqual(Comparable left, Comparable right) {
    if (left == null || right == null || (left.compareTo(right) > 0)) {
        String msg = "["+left+"] is not less than ["+right+"]";
        throw new RuntimeException("assertLessOrEqual: " + msg);
    }
}

3 个答案:

答案 0 :(得分:12)

这也适用于Comparable类型的子类:

public <T extends Comparable<? super T>> void assertLessOrEqual(T left, T right) {
  if (left == null || right == null || left.compareTo(right) > 0) {
    String msg = "["+left+"] is not less than ["+right+"]";
    throw new RuntimeException("assertLessOrEqual: " + msg);
  }
}

答案 1 :(得分:3)

这个怎么样:

public <T extends Comparable<T>> void assertLessOrEqual(T left, T right) {
  if (left == null || right == null || (left.compareTo(right) > 0)) {
    String msg = "["+left+"] is not less than ["+right+"]";
    throw new RuntimeException("assertLessOrEqual: " + msg);
  }
}

可能会使 little 位变得更加通用,但只会让它变得更复杂:)

答案 2 :(得分:2)

您无法通过泛型检查“left”的类型是否与运行时“right”的类型相同。 Java泛型是通过type erasure实现的,因此有关泛型类型参数的信息在运行时会丢失。

public <T extends Comparable<T>> void assertLessOrEqual(T left, T right) {
    if (left == null || right == null || (left.compareTo(right) > 0)) {
        String msg = "["+left+"] is not less than ["+right+"]";
        throw new RuntimeException("assertLessOrEqual: " + msg);
    }
}