Java - uppercase all ArrayList elements

In this article, we would like to show you how to uppercase all ArrayList elements in Java.

1. Using for loop

In this example, we use for loop to transform all the elements from letters ArrayList to uppercase.

import java.util.*;

public class Example {

    public static void main(String[] args) {
        List<String> letters = new ArrayList<>();
        letters.add("a");
        letters.add("b");
        letters.add("c");

        for (int i = 0; i < letters.size(); i++) {
            String newValue = letters.get(i).toUpperCase(Locale.ROOT);
            letters.set(i, newValue);
        }

        System.out.println(letters);
    }
}

Output:

[A, B, C]

2. Using for-each loop

In this example, we use for-each loop to transform all the elements from letters ArrayList to uppercase.

import java.util.*;

public class Example {

    public static void main(String[] args) {
        List<String> letters = new ArrayList<>();
        letters.add("a");
        letters.add("b");
        letters.add("c");

        for (String letter : letters) {
            String newValue = letter.toUpperCase(Locale.ROOT);
            letters.set(letters.indexOf(letter), newValue);
        }

        System.out.println(letters);
    }
}

Output:

[A, B, C]

3. Using streams

In this example, we use a stream with map() function to transform all the elements from letters ArrayList to uppercase and collect them in the new ArrayList - lettersToUpper.

import java.util.*;
import java.util.stream.Collectors;

public class Example {

    public static void main(String[] args) {
        List<String> letters = new ArrayList<>();
        letters.add("a");
        letters.add("b");
        letters.add("c");

        System.out.println("Before: " + letters);

        List<String> lettersToUpper = letters.stream()
                .map(String::toUpperCase)
                .collect(Collectors.toList());

        System.out.println("After:  " + lettersToUpper);
    }
}

Output:

Before: [a, b, c]
After:  [A, B, C]