Java String Manipulation: Common Methods You Should Know

String manipulation is one of the most fundamental operations in Java programming. Whether you’re processing user inputs, formatting output, or implementing algorithms, working with strings effectively is a critical skill. Java provides a rich set of methods for manipulating strings, making it easier to perform a wide range of tasks. In this blog, we’ll explore some of the most common string manipulation methods every Java developer should know.

1. Creating Strings

Strings in Java can be created in two ways:

• Using String literals:

  String str = "Hello, World!";

• Using the new keyword:

  String str = new String("Hello, World!");

While both methods achieve the same result, using string literals is generally preferred due to the string pool optimization in Java.

2. Checking String Length

To find the length of a string, use the length() method:

String str = "Java Programming";
System.out.println("Length: " + str.length());

Output:

Length: 16

3. Concatenation

You can combine strings using:

• The + operator:

  String firstName = "John";
  String lastName = "Doe";
  String fullName = firstName + " " + lastName;
  System.out.println(fullName);

• The concat() method:

  String fullName = firstName.concat(" ").concat(lastName);

4. Comparing Strings

Java offers several ways to compare strings:

• equals() Method: Compares two strings for equality, considering case sensitivity.

  String str1 = "Java";
  String str2 = "Java";
  System.out.println(str1.equals(str2)); // true

• equalsIgnoreCase() Method: Ignores case sensitivity.

  System.out.println(str1.equalsIgnoreCase("java")); // true

• compareTo() Method: Compares strings lexicographically.

  System.out.println(str1.compareTo("Jawa")); // Negative value

5. Extracting Substrings

The substring() method is used to extract a portion of a string:

String str = "Welcome to Java";
System.out.println(str.substring(11));       // "Java"
System.out.println(str.substring(0, 7));    // "Welcome"

6. Searching in Strings

• indexOf() Method: Finds the first occurrence of a character or substring.

  String str = "Programming in Java";
  System.out.println(str.indexOf('a')); // 12
  System.out.println(str.indexOf("Java")); // 16

• lastIndexOf() Method: Finds the last occurrence.

  System.out.println(str.lastIndexOf('a')); // 21

7. Replacing Characters or Substrings

Use the replace() method to replace characters or substrings:

String str = "Java is fun";
System.out.println(str.replace("fun", "powerful")); // "Java is powerful"

For advanced replacements, replaceAll() supports regular expressions:

String str = "123-456-7890";
System.out.println(str.replaceAll("\d", "*")); // "***-***-****"

8. Splitting Strings

The split() method divides a string into an array based on a delimiter:

String str = "apple,orange,banana";
String[] fruits = str.split(",");
for (String fruit : fruits) {
    System.out.println(fruit);
}

Output:

apple
orange
banana

9. Changing Case

• toUpperCase() Method: Converts all characters to uppercase.

  String str = "hello";
  System.out.println(str.toUpperCase()); // "HELLO"

• toLowerCase() Method: Converts all characters to lowercase.

  System.out.println(str.toLowerCase()); // "hello"

10. Trimming Whitespace

Use trim() to remove leading and trailing spaces:

String str = "  Java Programming  ";
System.out.println(str.trim()); // "Java Programming"

11. Checking String Emptiness

Java provides two methods to check if a string is empty or blank:

• isEmpty() Method: Returns true if the string has no characters.

  String str = "";
  System.out.println(str.isEmpty()); // true

• isBlank() Method (Java 11+): Returns true if the string is empty or contains only whitespace.

  String str = "   ";
  System.out.println(str.isBlank()); // true

12. String Formatting

The String.format() method allows you to create formatted strings:

String name = "Alice";
int age = 25;
String message = String.format("My name is %s and I am %d years old.", name, age);
System.out.println(message);

Output:

My name is Alice and I am 25 years old.

13. Joining Strings

From Java 8 onward, the String.join() method simplifies joining strings with a delimiter:

String result = String.join(", ", "Java", "Python", "C++");
System.out.println(result); // "Java, Python, C++"

Mastering these common string manipulation methods in Java can significantly improve your coding efficiency and clarity. Strings are integral to most Java applications, and knowing how to manipulate them effectively will make your code more robust and maintainable. Experiment with these methods in your projects to fully harness their power!

Got any favorite string methods we missed? Let us know in the comments below!