java - Java 泛型的乐趣

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("unchecked") 被认为是作弊）。

而且，也许，通过泛型检查 "left" 的类型是否与 "right" 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);
  }
}

它可能会变得更通用一点，但也只能让它变得更复杂:)

Answer 3

您不能通过泛型检查运行时“左”的类型是否与“右”的类型相同。Java 泛型是通过类型擦除实现的，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);
    }
}