For-each loop in Java

Difficulty Level : Easy
Last Updated : 03 May, 2021

Prerequisite: Decision making in Java
For-each is another array traversing technique like for loop, while loop, do-while loop introduced in Java5.

It starts with the keyword for like a normal for-loop.
Instead of declaring and initializing a loop counter variable, you declare a variable that is the same type as the base type of the array, followed by a colon, which is then followed by the array name.
In the loop body, you can use the loop variable you created rather than using an indexed array element.
It’s commonly used to iterate over an array or a Collections class (eg, ArrayList)

Syntax:

for (type var : array) 
{ 
    statements using var;
}

is equivalent to:

for (int i=0; i<arr.length; i++) 
{ 
    type var = arr[i];
    statements using var;
}

Java

// Java program to illustrate
// for-each loop
class For_Each    
{
    public static void main(String[] arg)
    {
        {
            int[] marks = { 125, 132, 95, 116, 110 };
             
            int highest_marks = maximum(marks);
            System.out.println("The highest score is " + highest_marks);
        }
    }
    public static int maximum(int[] numbers)
    {
        int maxSoFar = numbers[0];
         
        // for each loop
        for (int num : numbers)
        {
            if (num > maxSoFar)
            {
                maxSoFar = num;
            }
        }
    return maxSoFar;
    }
}

Output:

The highest score is 132

Limitations of for-each loop
decision-making

For-each loops are not appropriate when you want to modify the array:

for (int num : marks) 
{
    // only changes num, not the array element
    num = num*2; 
}

2. For-each loops do not keep track of index. So we can not obtain array index using For-Each loop

for (int num : numbers) 
{ 
    if (num == target) 
    {
        return ???;   // do not know the index of num
    }
}

3. For-each only iterates forward over the array in single steps

// cannot be converted to a for-each loop
for (int i=numbers.length-1; i>0; i--) 
{
      System.out.println(numbers[i]);
}

4. For-each cannot process two decision making statements at once

// cannot be easily converted to a for-each loop 
for (int i=0; i<numbers.length; i++) 
{
    if (numbers[i] == arr[i]) 
    { ...
    } 
}

5. For-each also has some performance overhead over simple iteration:

Java

/*package whatever //do not write package name here */
 
import java.io.*;
import java.util.*;
 
class GFG {
    public static void main (String[] args) {
        List<Integer> list = new ArrayList<>();
        long startTime;
        long endTime;
        for (int i = 0; i < 1000000; i++) {
            list.add(i);
        }
        // Type 1
        startTime = Calendar.getInstance().getTimeInMillis();
        for (int i : list) {
            int a = i;
        }
        endTime = Calendar.getInstance().getTimeInMillis();
        System.out.println("For each loop :: " + (endTime - startTime) + " ms");
         
        // Type 2
        startTime = Calendar.getInstance().getTimeInMillis();
        for (int j = 0; j < list.size(); j++) {
            int a = list.get(j);
        }
        endTime = Calendar.getInstance().getTimeInMillis();
        System.out.println("Using collection.size() :: " + (endTime - startTime) + " ms");
         
        // Type 3
        startTime = Calendar.getInstance().getTimeInMillis();
        int size = list.size();
        for (int j = 0; j < size; j++) {
            int a = list.get(j);
        }
        endTime = Calendar.getInstance().getTimeInMillis();
        System.out.println("By calculating collection.size() first :: " + (endTime - startTime) + " ms");
     
        // Type 4
        startTime = Calendar.getInstance().getTimeInMillis();
        for(int j = list.size()-1; j >= 0; j--) {
            int a = list.get(j);
        }
        endTime = Calendar.getInstance().getTimeInMillis();
        System.out.println("Using [int j = list.size(); j > size ; j--] :: " + (endTime - startTime) + " ms");
    }
}
 
// This code is contributed by Ayush Choudhary @gfg(code_ayush)

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Related Articles:
For-each in C++ vs Java
Iterator vs For-each in Java
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