Java 将对象转换为数组
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Cast Object to Array
提问by Ryan Epp
So I have an Object which MIGHT be an array. It can also be primitive, or a string. If it is an array, it can be an array of literally anything.
所以我有一个对象，它可能是一个数组。它也可以是原始的或字符串。如果它是一个数组，那么它可以是任何字面上的数组。
I have no problem figuring out if it is an array but I can't seem to cast it into anything that I can iterate through to get the values out of.
我可以确定它是否是一个数组，但我似乎无法将其转换为任何可以迭代以获取值的内容。
// o is an object and clazz is the class of the o
if (clazz == Array.class) {
Class ofArray = o.getClass().getComponentType();
String arrayType = ofArray.getName(); // 'Double' for my test case
//ERROR: [D cannot be cast to [Ljava.lang.Object
Object[] objects = (Object[]) o;
}
My background is in ruby and php (where it would just work) and the static typing is messing with my head. Any ideas?
我的背景是 ruby 和 php（它可以正常工作），静态类型弄乱了我的头脑。有任何想法吗？
EDIT:
编辑：
This throws the error
这会引发错误
[D cannot be cast to [Ljava.lang.Object.
What am I missing?
我错过了什么？
if (o.getClass().isArray()) {
Object[] objects = (Object[]) o;
}
采纳答案by Vegard
If you do not want to make the switch for all primitive types you could do like this:
如果您不想为所有原始类型进行切换，您可以这样做：
if (ofArray.isPrimitive()) {
int length = Array.getLength(o);
for (int i = 0; i < length; i++) {
Object obj = Array.get(o, i);
System.out.println(obj);
}
}
else {
Object[] objects = (Object[]) o;
for (Object obj : objects) {
System.out.println(obj);
}
}
Edit: If you don't want to loop in two different places in your code use this method to convert the primitive arrays to an object array:
编辑：如果您不想在代码中的两个不同位置循环，请使用此方法将原始数组转换为对象数组：
static Object[] convertToObjectArray(Object array) {
Class ofArray = array.getClass().getComponentType();
if (ofArray.isPrimitive()) {
List ar = new ArrayList();
int length = Array.getLength(array);
for (int i = 0; i < length; i++) {
ar.add(Array.get(array, i));
}
return ar.toArray();
}
else {
return (Object[]) array;
}
}
回答by óscar López
This will work for arrays with elements that are sublcasses of Object:
这将适用于具有以下子类的元素的数组Object：
if (clazz.isArray()) {
Object[] objects = (Object[]) o;
for (Object obj : objects)
System.out.println(obj);
}
If you need to cast the array to an specific array type you could (ab)use instanceofbut for, say, just printing the contents as strings, an Object[]suffices.
如果您需要将数组转换为特定的数组类型，您可以 (ab) 使用，instanceof但例如，只需将内容打印为字符串，Object[]就足够了。
UPDATE
更新
If the array is of primitive types, you have no option but to test for each one and cast to the correct type, Object[]won't work for this case - but there aren't thatmany primitive types in Java, so it won't be a gigantic switch :) . This is what I mean:
如果数组是原始类型，你别无选择，只能测试每一个并转换为正确的类型，Object[]在这种情况下不起作用 - 但Java中没有那么多原始类型，所以它不会成为一个巨大的开关 :) 。这就是我的意思：
if (clazz.isArray()) {
if (clazz.getComponentType().equals(double.class)) {
double[] numbers = (double[]) o;
for (double d : numbers)
System.out.println(d);
}
}
回答by fjf2002
It's not enough to know your Objectis an array - you should also know the underlying type of the array elements. If your array elements are of primitive type, say double, you need to
仅仅知道你Object是一个数组是不够的——你还应该知道数组元素的底层类型。如果您的数组元素是原始类型，例如double，您需要
double[] doubleArray = (double[]) o;
This won't work:
这行不通：
Object[] objects = (Object[]) o;
回答by Ravi Thapliyal
You cannot type cast an Array of primitives to an Object[]
您不能将原始数组类型转换为 Object[]
if (clazz == Array.class) {
Class ofArray = o.getClass().getComponentType();
// String arrayType = ofArray.getName(); // 'Double' for my test case
if (ofArray instanceof double.class)
double[] doubles = (double[]) o;
for (double d: doubles)
System.out.println(d);
}
To create an Object[]without instanceofchecks
创建一个Object[]没有instanceof检查的
if (!(o instanceof Object[])) {
int len = Array.getLength(o);
Object[] objects = new Object[len];
for (int i = 0; i < len; i++)
objects[i] = Array.get (o, i);
for (Object obj: objects)
System.out.println(obj);
}
