Java解包参数列表 [英] Java unpacking argument lists

问题描述

这是另一个问题我如何用Java做这个？在Python中，我可以使用'*'符号解压缩参数，如下所示：

Here's another question of "How would I do this in Java?" In Python, I can use the '*' symbol to unpack arguments like so:

>>> range(3, 6)             # normal call with separate arguments
[3, 4, 5]
>>> args = [3, 6]
>>> range(*args)            # call with arguments unpacked from a list
[3, 4, 5]

Java支持使用 ... args 语法获取args列表，但有没有办法（可能使用Reflection库？）解压缩其他函数？

Java supports getting a list of args with ...args syntax, but is there a way (perhaps using the Reflection libraries?) to unpack those for some other function?

推荐答案

public void printStrings(String... strings)
{
   // the strings parameter is really a String[].
   // You could do anything to it that you normally
   // do with an array.
   for(String s : strings){
      System.out.println(s);
   }
}

可以像这样调用：

String[] stringArray = new String[10];
for(int i=0; i < stringArray.length; i++){
   stringArray[i] = "String number " + (i+1);
}

printStrings(stringArray);

... 语法真的是语法数组的糖。

The ... syntax is really syntactic sugar for arrays.

Java没有你描述的功能，但你可以用几种方法伪造它。

Java doesn't have the facility that you describe, but you could fake it several ways.

我认为最接近的近似意味着使用varargs重载你想要以这种方式使用的任何函数。

I think the closest approximation means overloading any function that you want to use in that fashion using varargs.

如果你有一些方法：

public void foo(int a, String b, Widget c) { ... }

你可以重载它：

public void foo(Object... args) {
    foo((Integer)args[0], (String)args[1], (Widget)args[2]);
}

但这真的很笨拙且容易出错并难以维护。

But this is really clumsy and error prone and hard to maintain.

更一般地说，你可以使用反射来使用任何参数调用任何方法，但它也有很多陷阱。这是一个错误的，不完整的例子，说明它如何变得非常快：

More generically, you could use reflection to call any method using any arguments, but it's got a ton of pitfalls, too. Here's a buggy, incomplete example of how it gets ugly really fast:

public void call(Object targetInstance, String methodName, Object... args) {
    Class<?>[] pTypes = new Class<?>[args.length];
    for(int i=0; i < args.length; i++) {
        pTypes[i] = args[i].getClass();
    }
    Method targetMethod = targetInstance.getClass()
              .getMethod(methodName, pTypes);
    targetMethod.invoke(targetInstance, args);
}

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