Math.random() * (rangeR - rangeL + 1) + rangeL 返回的是double，double可以强转成Object没问题，但是不能强转成Integer。你的obj传的肯定不是Double.class：）
实际上，对于这个函数，在Java中是不建议写成泛型函数的。Java的泛型本身就没有那么灵活。所以即使在标准库中很多地方也不使用泛型。尤其是只限定数字类型时。（对于你的这个例子，就是限定数字类型。因为根据你的函数语义，并不是生成随机的可比较元素的数组。比如字符串是可比较的，但字符串无法在int rangeL到int rangeR之间。）
比如Math.abs，取绝对值，Java标准库是怎么实现的呢？答案是这样的：根本不用泛型！：）
/**
* Returns the absolute value of an {@code int} value.
* If the argument is not negative, the argument is returned.
* If the argument is negative, the negation of the argument is returned.
*
* <p>Note that if the argument is equal to the value of
* {@link Integer#MIN_VALUE}, the most negative representable
* {@code int} value, the result is that same value, which is
* negative.
*
* @param a the argument whose absolute value is to be determined
* @return the absolute value of the argument.
*/
public static int abs(int a) {
return (a < 0) ? -a : a;
}
/**
* Returns the absolute value of a {@code long} value.
* If the argument is not negative, the argument is returned.
* If the argument is negative, the negation of the argument is returned.
*
* <p>Note that if the argument is equal to the value of
* {@link Long#MIN_VALUE}, the most negative representable
* {@code long} value, the result is that same value, which
* is negative.
*
* @param a the argument whose absolute value is to be determined
* @return the absolute value of the argument.
*/
public static long abs(long a) {
return (a < 0) ? -a : a;
}
/**
* Returns the absolute value of a {@code float} value.
* If the argument is not negative, the argument is returned.
* If the argument is negative, the negation of the argument is returned.
* Special cases:
* <ul><li>If the argument is positive zero or negative zero, the
* result is positive zero.
* <li>If the argument is infinite, the result is positive infinity.
* <li>If the argument is NaN, the result is NaN.</ul>
* In other words, the result is the same as the value of the expression:
* <p>{@code Float.intBitsToFloat(0x7fffffff & Float.floatToIntBits(a))}
*
* @param a the argument whose absolute value is to be determined
* @return the absolute value of the argument.
*/
public static float abs(float a) {
return (a <= 0.0F) ? 0.0F - a : a;
}
/**
* Returns the absolute value of a {@code double} value.
* If the argument is not negative, the argument is returned.
* If the argument is negative, the negation of the argument is returned.
* Special cases:
* <ul><li>If the argument is positive zero or negative zero, the result
* is positive zero.
* <li>If the argument is infinite, the result is positive infinity.
* <li>If the argument is NaN, the result is NaN.</ul>
* In other words, the result is the same as the value of the expression:
* <p>{@code Double.longBitsToDouble((Double.doubleToLongBits(a)<<1)>>>1)}
*
* @param a the argument whose absolute value is to be determined
* @return the absolute value of the argument.
*/
public static double abs(double a) {
return (a <= 0.0D) ? 0.0D - a : a;
}
