英文:
Null Pointer Exception (Looping through an array of objects)
问题
我有一段时间没有使用Java了，所以有些生疏。我有一个返回对象数组的方法。在我的主程序中，我创建了一个新的对象数组，并将这个新的对象数组设置为方法的返回数组。类似这样：
Obj[] main_arr = new Obj[100];main_arr = method(x);for (int i = 0; i < main_arr.length; i++) {if (main_arr[i].number == 1) { // 错误似乎在这里// 做一些操作} else {// 做一些操作}}
我试图遍历 main_arr 并访问这个对象数组中的内容，但是我得到了一个空指针异常。我已经使用调试工具查看过了，main_arr 似乎有正确的内容。有任何想法是为什么吗？提前谢谢你！
英文:
I haven't used Java in a while so I'm rusty. I have a method that returns an array of objects. In my main, I created a new object array and set that new array of objects to the return array of the method. Something like this:
Obj[] main_arr = new Obj[100];main_arr = method(x);for (int i = 0; i < main_arr.length; i ++){if(main_arr[i].number == 1) { // the error seems to be here// do some stuff}else {// do some stuff}}
I am trying to loop through main_arr and access the things in this object array, however I get a Null Pointer Exception. I've been in the debugger tool and main_arr seems to have the correct content. Any ideas why? Thank you in advance!
答案1
得分: 1
一些 main_arr 中的元素是空的。
这可能发生在，例如，main_arr 有 100 个元素，但只有前 10 个实际上被赋值了值。
英文:
Some elements of main_arr are null.
This could happen, for example, if main_arr has 100 elements but only the first 10 were actually assigned a value.
答案2
得分: 0
"main_arr.length()" 不是正确的写法，应该是 "main_arr.length"。
英文:
It's main_arr.length() not main_arr.length
答案3
得分: 0
Java数组对象没有获取其长度的方法。您需要使用'数组长度属性'，如下所示：
int arrayLength = myArray.length;for (int i = 0; i <= arrayLength - 1; i++) {if (myArray[i] == whatever) {//做一些操作}}
来源：https://www.edureka.co/blog/array-length-in-java/
英文:
Java Array Object does not have a method to get its length. Youneed to use the ‘array length attribute’, like this:
int arrayLength = myArray.length;for (int i = 0; i <= arrayLength - 1; i++) {if (myArray[i] == whatever) {//do some job}}
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