用Java打印数组 [英] Print arrays in Java

问题描述

我正在编写一个方法来打印它传递的每个Object。通过为对象调用 Object.toString（）方法可以正常工作，但不适用于数组。我可以通过 Object.getClass（）。isArray（）方法找出它是否是一个数组，但我不知道如何投射它。

I'm writing a method that prints every Object it get passed. This works fine by calling the Object.toString() method for the object but doesn't works for arrays. I can find out whether it is an Array with the Object.getClass().isArray() method, but I don't know how to cast it.

int[] a;
Integer[] b;

Object aObject = a;
Object bObject = b;

// this wouldn't work
System.out.println(Arrays.toString(aObject));
System.out.println(Arrays.toString(bObject));

推荐答案

如果您不知道可以投的类型对象 Object [] 并打印出来（确定它确实是一个数组后可以转换为 Object [] ）。如果它不是 Object [] 的实例，则使用 reflection 创建 Object [] 首先打印：

If you don't know the type you can cast the object to Object[] and print it like this (after making sure it is indeed an array and can be cast to Object[]). If it is not an instance of Object[] then use reflection to create an Object[] first and then print:

private void printAnyArray(Object aObject) {
    if (aObject.getClass().isArray()) {
        if (aObject instanceof Object[]) // can we cast to Object[]
            System.out.println(Arrays.toString((Object[]) aObject));
        else {  // we can't cast to Object[] - case of primitive arrays
            int length = Array.getLength(aObject);
            Object[] objArr = new Object[length];
            for (int i=0; i<length; i++)
                objArr[i] =  Array.get(aObject, i);
            System.out.println(Arrays.toString(objArr));
        }
    }
}

测试：

printAnyArray(new int[]{1, 4, 9, 16, 25});
printAnyArray(new String[]{"foo", "bar", "baz"});

输出：

[1, 4, 9, 16, 25]
[foo, bar, baz]

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