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Common String Operations in Java

By IncludeHelp Last updated : January 29, 2024

Strings in Java

String is a class in java, which provides some of the predefined methods that make string based problem solutions easier. We don’t need to write code for every operation, we have to just use its methods.

In this post, we are going to learn some of the most useful methods of the string.

Declaring and assigning value to string objet

There can be two different ways to declare and assign a string to an object in Java.

Declaration and then assignment

String msg;	//declaration
msg = "Hello world"; // assignment

Declaration with initialization

String msg = "Hello world";

Checking equality of Java strings

The s1.equals(s2) method is used to compare two strings; it returns boolean values ‘true’/ ‘false’. If s1 and s2 are exactly same it returns ‘true’ otherwise it returns ‘false’.

Example

public class Main {
  public static void main(String[] args) {
    String s1 = "Hello world";
    String s2 = "Hello world";
    
    System.out.println(s1.equals(s2));
  }
}

Both strings are exactly same, so the function will returns 'true'.

Checking equality of Java strings by ignoring case

The s1.equalsIgnoreCase(s2) method is used to compare two strings but it ignores the case, it returns boolean values ‘true’/ ‘false’. If s1 and s2 are same (by ignoring the case) it returns ‘true’ otherwise it returns ‘false’.

Example

public class Main {
  public static void main(String[] args) {
    String s1 = "Hello world";
    String s2 = "HELLO world";
    System.out.println(s1.equalsIgnoreCase(s2));
  }
}

In this case, strings are same but characters are not in same case, still this function will return ‘true’.

Getting length of Java strings

The s1.length() method returns the length of the string s1 i.e. total number of characters of the string.

Example

public class Main {
  public static void main(String[] args) {
    String s1 = "Hello world!";
    System.out.println(s1.length());
  }
}

Total number of characters in the string "Hello world!" are 12. Therefore, this function will return 12.

Getting characters from Java string

The s1.charAt(N) method is used to get the character from N^th index of the string. Remember, string’s index starts from 0.

Example

public class Main {
  public static void main(String[] args) {
    String msg = "Hello world";
    System.out.println(msg.charAt(0));
    System.out.println(msg.charAt(6));
  }
}

Output of this example with be "H" and "w" because "H" is at the 0^th index and "w" is at the 6^th index.

Read more: Java String | String.charAt(index) Method with Example

Getting starting index of a substring

The s1.indexOf(s2) method is used to get the starting index of any substring. Here, if substring s2 exists in the string s1, it will return starting position (index) of substring s2. If substring does not exist in the string, it returns -1.

Example 1: If substring exists in the string

public class Main {
  public static void main(String[] args) {
    String msg = "Hello world";
    System.out.println(msg.indexOf("world"));
  }
}

Output will be 6, because substring "world" initial index starts from 6^th in the string "Hello world".

Example 2: If substring does not exist in the string

public class Main {
  public static void main(String[] args) {
    String msg = "Hello world";
    System.out.println(msg.indexOf("Hi"));
  }
}

Output will be -1, because substring "Hi" does not exist in the string "Hello world".

Checking substring in a Java string

The s1.substring(N,M) method is used to get the substring from the string. Here, function substring() will return the substring starting from N^th index to (M-1)^th index.

Let suppose value of N is 6 and value of M is 11, then function will return 6^th, 7^th, 8^th, 9^thth and 10^th character, it does not consist M^th character.

Example

public class Main {
  public static void main(String[] args) {
    String msg = "Hello world!";
    System.out.println(msg.substring(6, 11));
  }
}

Output will be "world".

Comparing Java strings

The s1.compareTo(s2) method is used to compare two strings, if both strings are same it returns 0, if string s1 is less than s2 it returns negative value, if string s2 is less than string s1 it returns positive value. Negative and positive value depends on the difference in the ASCII codes of first dissimilar characters.

Example

public class Main {
  public static void main(String[] args) {
    String s1, s2;

    s1 = "Hello";
    s2 = "Hello";
    System.out.print(s1.compareTo(s2));

    s1 = "Hello";
    s2 = "HELLO";
    System.out.println(s1.compareTo(s2));

    s1 = "Hello";
    s2 = "World";
    System.out.println(s1.compareTo(s2));
  }
}

Output

0
32
-15

Converting Java strings to uppercase

The s1.toUpperCase() method returns uppercase string.

Example

public class Main {
  public static void main(String[] args) {
    String msg = "Hello World!";
    System.out.println(msg.toUpperCase());
  }
}

Output will be "HELLO WORLD!".

Converting Java strings to lowercase

The s1.toLowerCase() method returns lowercase string.

Example

public class Main {
  public static void main(String[] args) {
    String msg = "Hello World!";
    System.out.println(msg.toLowerCase());
  }
}

Output will be "hello world!".

Trimming Java strings

The s1.trim() method returns the trimmed string after removing leading and trailing spaces.

Example

public class Main {
  public static void main(String[] args) {
    String msg = " Hello world! ";
    System.out.println(msg.trim());
  }
}

Output will be "Hello world!".