玩转Java泛型(Fun with Java generics)

任何人都知道如何写下面使用泛型，避免编译器警告的代码段？ （@SuppressWarnings（ “未登记”）被认为是作弊）。

而且，也许，经由类型“左”仿制药检查是一样的“正确”的类型？

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:

这适用于可比类型太多的子类：

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);
  }
}

这也许可以做出更一般的一点点 ，但只能通过使它更加复杂了:)

Answer 3:

您不能通过泛型检查的“左”的类型是一样的“正确”在运行时类型。 Java泛型是通过实现类型擦除 ，所以对一般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);
    }
}

文章来源: Fun with Java generics