Java – Check if a String contains a substring

By mkyong | Updated: April 19, 2019

Viewed: 1,747 (+19 pv/w)

Tags: java string

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

References

• String.contains() JavaDocs
• String.indexOf() JavaDocs