如何在java中查找数组中的元素数量？
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How to find number of element in an Array in java?
提问by Vid
I want to know that how can i find the number of element in the normal array in java. For example if i have an int array with size 10 and i have inserted only 5 element. Now, i want to check the number of element in my array? Below is the code for more clarification. Please help
我想知道如何在java中找到普通数组中的元素数。例如，如果我有一个大小为 10 的 int 数组，并且我只插入了 5 个元素。现在，我想检查数组中的元素数量？以下是更多说明的代码。请帮忙
public static void main(String[] args) {
int [] intArray = new int[10];
char [] charArray = new char[10];
int count = 0;
for(int i=0; i<=5; i++) {
intArray[i] = 5;
charArray[i] = 'a';
}
for(int j=0; j<=intArray.length; j++) {
if(intArray[j] != null) {
count++;
}
}
System.out.println("int Array element : "+ count);
}
采纳答案by Ascalonian
Check out Collection.frequency(). This will count how many times the specific Object (in this case null) appears in the Collection.
退房Collection.frequency()。这将计算特定对象（在本例中null）在集合中出现的次数。
Below is just an example to help you along
下面只是一个例子来帮助你
String[] array = new String[5];
array[0] = "This";
array[1] = null;
array[2] = "is";
array[3] = null;
array[4] = "a test";
int count = Collections.frequency(Arrays.asList(array), null);
System.out.println("String: " + count + " items out of " + array.length + " are null");
int[] iArray = new int[3];
iArray[0] = 0;
iArray[1] = 1;
iArray[2] = 2;
List<Integer> iList = new ArrayList<>();
for (int i : iArray) {
iList.add(i);
}
int iCount = Collections.frequency(iList, 0);
System.out.println("Int: " + iCount + " items out of " + iArray.length + " are zero");
char[] cArray = new char[3];
cArray[0] = 'c';
cArray[1] = ' ';
cArray[2] = 'a';
List<Character> cList = new ArrayList<>();
for (char c : cArray) {
cList.add(c);
}
int cCount = Collections.frequency(cList, ' ');
System.out.println("Char: " + cCount + " items out of " + cArray.length + " are ' '");
Output:
输出：
String: 2 items out of 5 are null
Int: 1 items out of 3 are zero
Char: 1 items out of 3 are ' '
字符串：5 项中有 2 项为空
Int：3 项中有
1 项为零字符：3 项中有 1 项是 ' '
回答by Arnaud Denoyelle
The code is wrong. You declare a int[]: this cannot contain null values so this statement will not compile :
代码错了。你声明了一个int[]: this 不能包含空值，所以这个语句不会编译：
if(intArray[j] != null) {
Then, if you want to store many items but you don't know howmany, you should use a Collection, for example ArrayList
然后，如果你想存储很多项目但你不知道有多少，你应该使用一个Collection，例如ArrayList
List<Integer> ints = new ArrayList<Integer>(); //Or new ArrayList<>(); - Java7
Then, you can have the size with :
然后，您可以使用以下尺寸：
ints.size();
Now, if you reallywant to use an array, then you can for example count the number of non-zero values :
现在，如果你真的想使用一个数组，那么你可以例如计算非零值的数量：
for(int j=0; j<=intArray.length; j++) {
if(intArray[j] != 0) {
count++;
}
}
Or better in Java 7:
或者在Java 7 中更好：
for(int i : intArray) {
if(i!=0) {
count++;
}
}
Even better in Java 8:
在Java 8 中甚至更好：
Arrays.stream(intArray).filter(i -> i !=0).count();
回答by Jared Mackey
You could change your first loop to something like this:
您可以将第一个循环更改为如下所示：
for(int i=0; i<=5; i++) {
intArray[i] = 5;
charArray[i] = 'a';
count++;
}
Or better yet, instead of using an array use an ArrayList. Here is an example of how arraylists work.
或者更好的是，不要使用数组，而是使用 ArrayList。下面是一个数组列表如何工作的例子。
ArrayList<Integer> intList = new ArrayList<Integer>();
ArrayList<Character> charList = new ArrayList<Character>();
for (int i = 0; i < 5; i++){
intList.add(5);
charList.add('a');
}
System.out.println("int list element : " + intList.size());
ArrayList's are dynamic and .size()will only return the size of items currently in the arraylist.
ArrayList 是动态的，.size()只会返回当前在 arraylist 中的项目的大小。
回答by Hayden
If you want to implement your own solution for counting elements in an array, you can always implement your own wrapper class with the arrayin it if you want to.
如果您想实现自己的解决方案来计算数组中的元素，您可以随时使用arrayin实现自己的包装类。
public class classWithArray {
private int[] arr;
private int count;
public classWithArray(int arrLength) {
arr = new int[5];
count = 0;
}
public void add(int num) {
arr[count] = num;
count++;
}
public int getCount() {
return count;
}
public int getElement(int index) {
return arr[index];
}
// Add other wrapper methods.
}
You can make the arrayof a Generictype (I don't know much about Javafor that though) to make it work for any data type.
您可以创建array一个Generic类型（Java尽管我对此知之甚少）以使其适用于任何数据类型。
回答by Aamir M Meman
Well, We can use count for non-zero elements in the array,The Code is Below::
好吧，我们可以对数组中的非零元素使用计数，代码如下：
public class SomeElementOfArrayUsingCount{
public static void main(String[] args){
double total;//The sum of non-zero numbers in the Array.
total=0;
double average;//The average of non-zero numbers.
int i;
double count;//The number of non-zero numbers.
count = 0;
int[] list;
list = new int[5];//make a container of 5.
list[0]=2;
list[1]=4;
list[2]=4;
list[3]=5;
list[4]=2;
for(i=0;i<list.length;i++){
if(list[i]!=0){
total = total + list[i];//Add element to the array
count = count + 1;//and Count it
}
}
if(count==0){
System.out.println("There were no non-zero elements");
}
else {
average = total/count;//Divide by number of items
System.out.println("The average is " + average + " the total count is " + count);
}
}
}
