你如何找到数组中元素的索引？

Question

import java.util.Scanner;
public class Lab6a
{
    public static void main (String args[])
    {
        int a[] = {34, 29, 16, 3};
        for (int i=0; i>=0; i--)
        {
            System.out.println("a[i] = " + a[1]);
        }
    }
}

This will print out 29. I need a way to search my array for 29 and return it's index and then store the index as an integer

Answer 1

You can find index of particular value like this.!

Integer[] array = {1,2,3,4,5,6};

Arrays.asList(array).indexOf(4);

and also change for loop in your code

for (int i = 0; i < array.length; i++)

or

 for (int i = array.length -1 ; i>=0; i--)

Answer 2

import java.util.Scanner;
    public class Lab6a
    {
        public static void main (String args[])
        {
            int i;
            int a[] = {34, 29, 16, 3};
            for (i=0; i<=3; i++)
            {
                System.out.println("a[i] = " + i);
            }
        }
    }

You can also write for(i=0;i<a.length;i++) at the needed postion.This will iterate from 0 to length - 1(ie 4) .

Notes: length() is a method on java.lang.String and works only on arrays.However if you are using collections like arraylists you can also use size() which is a method specified in java.util.Collection .Actually size works well to iterate through objects and is flexible unlike length ,which is used mostly with constants.

Answer 3

You can try something like this if you want to keep your array.

int a[] = {34, 29, 16, 3};
int i=0;
while (i<a.length)
{
    if(a[i] == 29) {
        System.out.println("index of 29 is " + i);
        break;
    }
    i++;
}

Answer 4

import java.util.Scanner;
public class Lab6a
{
    public static void main (String args[])
    {
        int a[] = {34, 29, 16, 3}; // the array
        for (int i = 0; i < a.length; i++) // check for each position in array
        {
            System.out.println(a[i] + " = " + a.indexOf(a[i])); // 34 = 0, 29 = 1 etc.
        }
    }
}

Answer 5

As far as I understand, you have several code mistakes. Try this code (put it in your main function). Most likely, it should work just fine.

int a[] = {34, 29, 16, 3};
int index = -1;
for (int i = 0; i < a.length; i++)
{
    if (a[i] ==  29)
    {
        index = i;
        System.out.print("a[" + i + "] = " + a[i]);
    }
}
if (index == -1)
    System.out.print("Such array element not found.")

The index variable will store the index value of the element you have found. If it was not found, -1 will be stored there.