What Is String Data Structure in Java?


Scott Campbell

A string is a data structure in Java that represents a sequence of characters. It is one of the most commonly used data types in programming, as it allows us to work with textual data efficiently. In Java, strings are represented by the String class.

Creating Strings

To create a string in Java, you can use either the String class constructor or by using string literals.

Using String Constructor

You can create a string by calling the String class constructor and passing the desired sequence of characters as an argument. For example:

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

The above code creates a new string object with the value “Hello World”.

Using String Literals

In Java, you can also create strings using string literals. A string literal is a sequence of characters enclosed within double quotes. For example:

    String str = "Hello World";

The above code creates a new string object with the value “Hello World”. Using string literals is more convenient and widely used.

String Operations

The String class in Java provides various methods to perform operations on strings.


The concatenation operation allows you to combine two or more strings into one. In Java, you can use the ‘+’ operator or the concat() method to concatenate strings. For example:

    String str1 = "Hello";
    String str2 = "World";
    // Using '+' operator
    String result1 = str1 + ", " + str2; // Output: "Hello, World"
    // Using concat() method
    String result2 = str1.concat(", ").concat(str2); // Output: "Hello, World"


The length() method returns the length of a string, which is the number of characters it contains. For example:

    String str = "Hello World";
    int length = str.length(); // Output: 11


The substring() method allows you to extract a portion of a string. It takes two parameters – the starting index and the ending index (exclusive) of the substring. For example:

    String str = "Hello World";
    String substring = str.substring(6, 11); // Output: "World"

String Comparison

You can compare strings in Java using the equals() method. The equals() method compares two strings and returns true if they are equal, and false otherwise. For example:

    String str1 = "Hello";
    String str2 = "World";
    boolean isEqual = str1.equals(str2); // Output: false

String Manipulation

The String class provides several methods for manipulating strings:

  • ToUpperCase(): Converts all characters in a string to uppercase.
  • ToLowerCase(): Converts all characters in a string to lowercase.
  • Trim(): Removes leading and trailing whitespace from a string.
  • Replace(): Replaces all occurrences of a specified character or substring with another character or substring.

String Immutability

One important thing to note about strings in Java is that they are immutable, which means that their values cannot be changed once they are created. If you perform any operation on a string, such as concatenation or manipulation, it doesn’t modify the original string, but instead returns a new string with the modified value.

For example:

    String str = "Hello";
    String modifiedStr = str.concat(" World"); // Output: "Hello World"
    System.out.println(str); // Output: "Hello"
    System.println(modifiedStr); // Output: "Hello World"


In conclusion, strings are an essential data structure in Java for working with textual data. They can be created using either the String class constructor or string literals.

String operations such as concatenation, length retrieval, and substring extraction can be performed using various methods provided by the String class. It’s important to remember that strings are immutable in Java, and any operation on a string returns a new string object.

By understanding and utilizing the features of the String class effectively, you can manipulate and process textual data efficiently in your Java programs.

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