Java String Methods

The String class has many methods. These are the ones you will use most. All the examples use this text.

Basic methods

public class Main {
    public static void main(String[] args) {
        String s = "Learn Java Step by Step";

        System.out.println(s.length());            // number of characters
        System.out.println(s.charAt(0));           // first character
        System.out.println(s.toUpperCase());
        System.out.println(s.toLowerCase());
        System.out.println(s.isEmpty());
        System.out.println(s.contains("Java"));
        System.out.println(s.startsWith("Learn"));
        System.out.println(s.endsWith("Step"));
    }
}

Find and cut

public class Find {
    public static void main(String[] args) {
        String s = "Learn Java Step by Step";

        System.out.println(s.indexOf("Java"));        // first position
        System.out.println(s.indexOf("Step"));
        System.out.println(s.lastIndexOf("Step"));    // last position
        System.out.println(s.indexOf("Python"));      // -1 if not found
        System.out.println(s.substring(6));           // from index 6
        System.out.println(s.substring(6, 10));       // from 6 to before 10
    }
}

The positions start at 0. For substring(start, end) the end index is not included.

Change text

public class Change {
    public static void main(String[] args) {
        String s = "I like Java. Java is fun.";
        System.out.println(s.replace("Java", "Python"));
        System.out.println(s.replaceFirst("Java", "C"));
        System.out.println("  hello  ".trim() + "|");
        System.out.println("  hello  ".strip() + "|");
        System.out.println("ab".repeat(3));
    }
}

Split and join

public class Split {
    public static void main(String[] args) {
        String csv = "red,green,blue";
        String[] colors = csv.split(",");
        System.out.println(colors.length);
        for (String c : colors) {
            System.out.println(c);
        }
        System.out.println(String.join(" | ", colors));
    }
}

Format text

public class Format {
    public static void main(String[] args) {
        String name = "Riya";
        int age = 21;
        double marks = 87.456;

        System.out.println(String.format("%s is %d years old", name, age));
        System.out.printf("Marks: %.2f%n", marks);     // 2 decimal places
        System.out.println("%s scored %.1f".formatted(name, marks));
    }
}

Format	Meaning
%s	String
%d	Whole number
%f, %.2f	Decimal number (with 2 digits after the point)
%n	New line (works on every system)
%c	Character
%b	Boolean

Check the characters

public class Chars {
    public static void main(String[] args) {
        String s = "Java25";
        int letters = 0, digits = 0;
        for (char c : s.toCharArray()) {
            if (Character.isLetter(c)) letters++;
            if (Character.isDigit(c)) digits++;
        }
        System.out.println("Letters: " + letters + ", digits: " + digits);
        System.out.println(new StringBuilder("stressed").reverse());
    }
}

Quick list

Method	Use
length()	Number of characters
charAt(i)	Character at a position
substring(a, b)	Part of the text
indexOf(x)	Position of the first x, -1 when missing
equals(x), equalsIgnoreCase(x)	Compare the text
contains(x), startsWith(x), endsWith(x)	Check the text
replace(a, b)	Replace text
split(x)	Break into an array
trim(), strip()	Remove the spaces at both ends
toUpperCase(), toLowerCase()	Change the case
isEmpty(), isBlank()	Empty check
repeat(n)	Repeat the text

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