Java泛型和数字类型 [英] Java generics and numeric types

问题描述

  class MyClass {
 $ b我想创建一个通用的方法$ b static< T extends Number> T sloppyParseNumber（String str）{
 try {
 return T.valueOf（str）; 
} catch（Exception e）{
 return（T）0; 
 
 
 
 $ $ $ 
 $ b $现在上面不编译为原因有两个：没有 Number.valueOf（）方法，0不能转换为 T 。
 
 
 
示例用法： 
 
 
 字符串值=0.00000001; 
 
 System.out.println（Double：+ MyClass。< Double> sloppyParseNumber（value））; 
 System.out.println（Float：+ MyClass。< Float> sloppyParseNumber（value））; 
 
 double d = MyClass.sloppyParseNumber（value）; 
 float f = MyClass.sloppyParseNumber（value）; 
  
在Java中实现上述通用方法可能吗？如果是，如何？如果不是，有什么好的替代方法？
 
 
 
 
 
 
编辑：似乎有一些可能的重复项，但我没有找到一个，其中涵盖了这一点。我希望有一些技巧可以解决，这将允许这两个操作：将字符串解析为 Number 子类，并为数字返回0值子类。
解决方案
我同意TofuBeer 100％但是如果你想避免冗长的话，这应该也是这样：
  static< T extends Number> T sloppyParseNumber（String str，Class< T> class）{
 
 if（clas == null）throw new NullPointerException（clas is null）; 
 
 {b 
 $ b if（clas.equals（Integer.class））{
 return（T）Integer.valueOf（str）; 
} 
 else if（clas.equals（Double.class））{
 return（T）Double.valueOf（str）; 
 
 // 
 $ b $ catch（NumberFormatException | NullPointerException ex）{
 //强制使用有效参数调用
 return sloppyParseNumber（0 ，clas）; 
} 
 
抛出新的IllegalArgumentException（无效的分类+ clas）; 
 
 
  
但纯粹来自 T ，你不能在运行时获得类型。
 
I'd like to create a generic method which does effectively this:
class MyClass {

    static <T extends Number> T sloppyParseNumber(String str) {
        try {
            return T.valueOf(str);
        } catch (Exception e) {
            return (T)0;
        }
    }
}
Now above does not compile for two reasons: there's no Number.valueOf() method and 0 can't be cast to T.

Example usage:
String value = "0.00000001";

System.out.println("Double: " + MyClass.<Double>sloppyParseNumber(value));
System.out.println("Float: " + MyClass.<Float>sloppyParseNumber(value));

double d = MyClass.sloppyParseNumber(value);
float f = MyClass.sloppyParseNumber(value);
Is implementing above generic method possible with Java?  If yes, how?  If no, what's a good alternative approach?



Edit: there seems to be a few possible duplicates, but I did not find one, which covers exactly this. I'm hoping there's some trick to pull, which would allow these two operations: parse string to a Number subclass, and return 0 value for a Number subclass.
解决方案
I agree 100% with TofuBeer. But in case you wish to avoid verbosity for time sake, this should also do:
static <T extends Number> T sloppyParseNumber(String str,Class<T> clas) {

    if (clas == null) throw new NullPointerException("clas is null");

    try {

        if(clas.equals(Integer.class)) {
            return (T) Integer.valueOf(str);
        }
        else if(clas.equals(Double.class)) {
            return (T) Double.valueOf(str);
        }
        //so on

    catch(NumberFormatException|NullPointerException ex) {
        // force call with valid arguments
        return sloppyParseNumber("0", clas);
    }

    throw new IllegalArgumentException("Invalid clas " + clas);

}
But purely from T, you cannot get the type at runtime.

                        
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