toUpperCase and trim

Learn transformations with toUpperCase() and trim().

toUpperCase and trim

To uppercase a String use toUpperCase(), to lowercase use toLowerCase(). To trim leading and trailing spaces use trim().

String s = "  Hello  ";
String clean = s.trim();           // "Hello"
String upper = clean.toUpperCase(); // "HELLO"

Strings are immutable; these methods return a new String, leaving the original untouched. You must assign the result to a variable.

Exercise Use trim and toUpperCase

Write a Main class with a main method. Assign " java " to String s. Assign s.trim() to String clean and clean.toUpperCase() to String upper. Print upper with println.

Show example solution

public class Main {
    public static void main(String[] args) {
        String s = "  java  ";
        String clean = s.trim();
        String upper = clean.toUpperCase();
        System.out.println(upper);
    }
}

Chaining transformations

You can call multiple transformations in a row; this is called chaining:

String result = s.trim().toUpperCase().substring(0, 3);

Here trim runs first, then toUpperCase, last substring. Each step produces a new String.

Chaining keeps code short but can hurt readability if overused. Long chains may be split for clarity.

Test yourself

What does String.toUpperCase() return?
- int
- char
- Same String
- New String
Show answer

New String — toUpperCase returns a new String, leaving the original untouched.
Match the methods

toUpperCase()

Uppercase
toLowerCase()

Lowercase
trim()

Trim spaces
length()

Length

Complete the trim call

String clean = s.____();

Show answer

String clean = s.trim();

Next lesson: String.format

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