Java返回索引（如果在数组中找到值）

Question

I am trying to find a value in an array and I know for sure that this value will exist only once, so i am trying to find the value and return the index of the array where it is stored, if not found return -1 This is what I am trying to do:

static Integer[] accs = new Integer[20];
 public static int search()
    {
        Integer[] numbers;
        numbers = accs;
        Integer key;
        Scanner sc = new Scanner(System.in);
         System.out.println("Enter the Account Number:");        
         key = sc.nextInt();

        for (Integer index = 0; index < numbers.length; index++)
      {
           if ( numbers[index] == key )
                 return index;  //We found it!!!
      }
     // If we get to the end of the loop, a value has not yet
     // been returned.  We did not find the key in this array.
     return -1;

    }

When I run this even though I know that the value exists in the array, nothing is being displayed. I debugged and then I found out that the Key variable is not having the value of what I typed. Is something wrong there?

Answer 1

Your array is storing Integer, which is a java Object, to test for equality of Java Object you need to call Object.equals method instead of == .

In your case I suggest you use an array of int instead of Integer , it is lighter in memory, support == and you are not using any of the features of Integer so you don't need them here.

Answer 2

You are checking for identity when checking with operator== (Are the two references point to the exact same object?) and not equality (do they equal each other?).

You should use int s (rather then Integer s) or change the condition to use the equals() method.

Answer 3

Integer is an object, so you have to make use of the equals method. Try numbers[index].equals(key).

Answer 4

java.util.Arrays.asList(accs).indexOf(key)  

要么

org.apache.commons.lang.ArrayUtils.indexOf(accs, key);

Answer 5

Make sure you understand the difference between object equality and object identity. You are using "==" to check if your value is in the array - this checks for identity, not for equality. Use numbers[index].equals(key) instead.

Answer 6

You need set value for each element before search. The statement below only declare new array with 20 element with value = null static Integer[] accs = new Integer[20]; Replace by: static Integer[] accs = new Integer[]{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}; and retest.

Regards,

Answer 7

initialize the array like this way static Integer[] accs = {3,5,15,6,4,32,9}; and call search() method in the main. your function work properly.

Answer 8

使用以下命令捕获用户输入BufferedReader br = new BufferedReader（new InputStreamReader（System.in））;