Java String contains() Method Examples

Java String contains() method returns true if this string contains the given character sequence.

Java String contains() method signature

String contains() method signature is:

public boolean contains(CharSequence s)

There are three classes that implements CharSequence interface.

1. String
2. StringBuffer
3. StringBuilder

Important Points for contains() method

• This utility method was introduced in Java 1.5
• It uses indexOf() method to check if this string contains the argument string or not.
• If the argument is null then NullPointerException will be thrown.
• This method is case sensitive. For example, "x".contains("X"); will return false.
• You can convert both the strings to lowercase for case insensitive operation. For example, "x".toLowerCase().contains("X".toLowerCase()); will return true.

String contains() Examples

1. Let’s look at a simple example where we pass String as an argument.

String s = "Hello World";

System.out.println(s.contains("Hello")); // true

2. We can create string objects using Unicode values. The unicode value of ‘H’ is ‘\u0048’.

System.out.println(s.contains("\u0048")); // true

3. Let’s look at an example with StringBuffer object as the argument.

System.out.println(s.contains(new StringBuffer("Hello"))); // true

4. Let’s look at an example with StringBuilder object as the argument.

System.out.println(s.contains(new StringBuilder("Hello"))); // true

5. The java.nio.CharBuffer class implements CharSequence interface. Let’s look at an example of contains() method with CharBuffer object as argument.

CharBuffer cb = CharBuffer.allocate(5);
cb.append('H');cb.append('e');cb.append('l');cb.append('l');cb.append('o');
cb.clear();
System.out.println(cb); // Hello
System.out.println(s.contains(cb)); // true

JShell Examples of contains() method

We can run above code snippets in JShell too.

jshell> String s = "Hello World";
s ==> "Hello World"

jshell> s.contains("Hello");
$20 ==> true

jshell> s.contains("\u0048");
$21 ==> true

jshell> s.contains(new StringBuffer("Hello"));
$22 ==> true

jshell> s.contains(new StringBuilder("Hello"));
$23 ==> true

jshell> import java.nio.CharBuffer;
   ...> 

jshell> CharBuffer cb = CharBuffer.allocate(5);
cb ==> 

jshell> cb.append('H');cb.append('e');cb.append('l');cb.append('l');cb.append('o');
$26 ==> 
$27 ==> 
$28 ==> 
$29 ==> 
$30 ==> 

jshell> cb.clear();
$31 ==> Hello

jshell> System.out.println(cb);
Hello

jshell> s.contains(cb)
$33 ==> true

jshell> 

References

• Oracle API Documentation