有趣的Java泛型

Question

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）。

并且，也许，通过泛型检查“左”的类型。与“正确”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);
    }
}

Answer 1

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);
  }
}

Answer 2

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);
  }
}

它可能会变得更加通用 little ，但只会使它变得更复杂：）

Answer 3

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泛型通过类型擦除实现，以便有关泛型类型参数的信息在运行时丢失。

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);
    }
}