Java – Check if a String contains a substring

In Java, we can use String.contains() to check if a String contains a substring.

1. String.contains() – Case Sensitive

package com.mkyong;
public class JavaExample1 {
    public static void main(String[] args) {
        String name = "mkyong is learning Java 123";
        System.out.println(name.contains("Java"));      // true
        System.out.println(name.contains("java"));      // false
        System.out.println(name.contains("MKYONG"));    // false
        System.out.println(name.contains("mkyong"));    // true
        if (name.contains("Java")) {
            System.out.println("Hello Java");
        } else {
            System.out.println("abc...");

Output

true
false
false
true
Hello Java

2. String.contains() – Ignoring Case

The idea is to convert all the strings and substring to lowercase before check with .contains()

package com.mkyong;
public class JavaExample2 {
    public static void main(String[] args) {
        String name = "mkyong is learning Java 123";
        System.out.println(containsIgnoreCase(name, "Java"));      // true
        System.out.println(containsIgnoreCase(name, "java"));      // true
        System.out.println(containsIgnoreCase(name, "MKYONG"));    // true
        System.out.println(containsIgnoreCase(name, "mkyong"));    // true
    public static boolean containsIgnoreCase(String str, String subString) {
        return str.toLowerCase().contains(subString.toLowerCase());

Output

true
true
true
true

3. indexOf()

3.1 Review the JDK String source code, the contains() uses indexOf() to check substring internally.

package java.lang;
	public boolean contains(CharSequence s) {
        return indexOf(s.toString()) >= 0;

3.2 So, we can also check the substring like this :

package com.mkyong;
public class JavaExample3 {
    public static void main(String[] args) {
        String name = "mkyong is learning Java 123";
        if (name.indexOf("Java") != -1) {
            System.out.println("Hello Java"); // print this
        } else {
            System.out.println("abc...");

Output

Hello Java