String. Practical Tasks

The call text.replace("a", "o"); compiles and runs without errors, yet text stays the same: strings in Java are immutable, and the new string the method returns is simply thrown away. Slips like this are caught fastest by practice, and that is what the exercises below are for.

This page collects 13 Java string exercises with solutions — practice problems on the methods of the String class, building a string with StringBuilder, formatting with String.format() and printf(), and regular expressions with Pattern and Matcher. The exercises go from simple to combined: String methods first, then StringBuilder and formatting, then regex, and finally the word and palindrome problems that mix several topics. Most have a solution on Patreon, and some have a video walkthrough. If you need a refresher first, read StringBuilder and StringBuffer in Java, String Formatting in Java and Regular Expressions in Java.

String Methods Practice

1. Write a method that takes any string as a parameter, for example “I like Java!!!”.
2. Print the last character of the string. Use the String.charAt() method.
3. Check whether your string ends with the substring “!!!”. Use the String.endsWith() method.
4. Check whether your string starts with the substring “I like”. Use the String.startsWith() method.
5. Check whether your string contains the substring “Java”. Use the String.contains() method.
6. Find the position of the substring “Java” in the string “I like Java!!!” with String.indexOf().
7. Replace every occurrence of the character a with o.
8. Convert the string to upper case with String.toUpperCase().
9. Convert the string to lower case with String.toLowerCase().

Video walkthrough →Solution on Patreon →

Build a String with StringBuilder

1. Given two numbers, for example 3 and 56, use StringBuilder.append() to build these strings:

   3 + 56 = 59
   3 - 56 = -53
   3 * 56 = 168

2. Replace the “=” sign with the word “equals” (for example, 3 + 56 equals 59). Use StringBuilder.replace().

Video walkthrough →Solution on Patreon →

Replace Every Second Occurrence of a Phrase

Write a method that replaces every second occurrence of “object-oriented programming” in a string (ignoring case) with “OOP”. For example, the string

Object-oriented programming is a programming language model organized around objects rather than "actions" and data rather than logic. Object-oriented programming blabla. Object-oriented programming bla.

must be converted to

Object-oriented programming is a programming language model organized around objects rather than "actions" and data rather than logic. OOP blabla. Object-oriented programming bla.

Solution on Patreon →

Find the Two Middle Characters of a String

Given a string of even length, return its two middle characters. For example:

• "string" → "ri"
• "code" → "od"
• "Practice" → "ct"

Solution on Patreon →

Student List with String.format()

Create a string using formatting: Student [surname] scored [grade] in [subject]. Write the formatting and the console output in a separate method that takes the surname, the grade and the subject name as parameters. Reserve 15 characters for the surname, 3 characters for the grade and 10 for the subject.

Example output:

Student Smith           scored 95  in Math
Student Brown           scored 87  in Physics
Student Johnson         scored 72  in Programming

Video walkthrough →Solution on Patreon →

Employee Salary Report with Formatting

Employee Report · part 1 of 1

1. Create an Employee class with the fields fullname and salary.
2. Create an array that contains several objects of this type.
3. Create a Report class with a static method generateReport(Employee[] employees) that prints the salary information of all employees.
4. Use string formatting: right-align salary and print it with 2 digits after the decimal point. You can add something of your own.

Solution on Patreon →

Simple Regular Expression: cab, ccab, cccab

Change the regular expression in the example so that it matches the strings cab, ccab and cccab.

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegexDemo2 {
    public static void main(String[] args) {
        Pattern pattern = Pattern.compile("a*b");
        Matcher matcher = pattern.matcher("aaab");
        boolean b = matcher.matches();
        System.out.println(b);
    }
}

For the strings cab, ccab and cccab the program must print true, and for ab it must print false.

Video walkthrough →Solution on Patreon →

Regular Expression for a Domain Name

Change the regular expression in the example so that reference1.org is also considered a valid link.

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegexDemo3 {
    public static void main(String[] args) {
        System.out.println(test("google.com"));
        System.out.println(test("reference1.ua"));
        System.out.println(test("reference1.org"));
    }

    public static boolean test(String testString) {
        Pattern pattern = Pattern.compile(".+\\.(com|ua|ru)");
        Matcher matcher = pattern.matcher(testString);
        return matcher.matches();
    }
}

Right now the program prints true, true, false. Expected output after the change:

true
true
true

Video walkthrough →Solution on Patreon →

Find All "Java X" Versions with Regex

Given a string:

String text = "Versions: Java  5, Java 6, Java   7, Java 8, Java 12.";

Find all substrings of the form “Java X”, where X is a version number, and print them. There may be several spaces between the word Java and the number.

Expected output:

Java  5
Java 6
Java   7
Java 8
Java 12

Video walkthrough →

Find the Word with the Fewest Distinct Characters

Find the word with the smallest number of distinct characters. A word may contain letters and digits. If there are several such words, find the first one. For example, in the string "fffff ab f 1234 jkjk" the word found must be "fffff".

Count the Words Made of Latin Letters Only

A sentence consists of several words separated by spaces, for example: "One two three one1 two2 123 naïve ". Find the number of words that contain only letters of the Latin alphabet (a–z and A–Z).

Expected result for the example: 3.

Find the Palindromes Among Numbers

A sentence consists of several words, for example: "If you have homework left, start with 1 unfinished assignment. 123 324 111 4554". Among the words that consist only of digits, find and print all palindromes — the words that read the same from left to right and from right to left.

Expected result for the example: 1, 111, 4554.

Shopping Receipt with Formatting

Online Store · part 3 of 3 · ← part 2

When a customer makes a purchase, print a report of the purchased products to the console. Use formatting. For example:

Product        Price
--------------------
Jeans        1500.78
Skirt        1000.56
Tie           500.78
--------------------
Total:       3002.12

Solution on Patreon →

What to Review Before You Start

These exercises rely on four topics: String methods, StringBuilder, format specifiers and regex basics. The table shows which exercises use each topic and links to the lesson where the method you need is explained with an example.

Where String Solutions Usually Go Wrong

Most wrong solutions to string exercises come not from complicated algorithms but from five typical slips: comparing with ==, going past the last index, using matches() instead of find(), an unescaped dot in a regex, and the default locale in String.format(). Check your code against this table before you submit it.