Introduction: Java String

In Java, a String is a class that represents a sequence of characters. It is part of the java.lang package and it is one of the most commonly used classes in Java. The String class is immutable, meaning that once a String object is created, its content cannot be changed.

Java is unique in supporting operator overloading exclusively for the String class. We can concatenate two strings using the + operator, as demonstrated by the expression “a” + “b” resulting in “ab.”

For effective string manipulation, Java provides two valuable classes: StringBuffer and StringBuilder. These classes allow for dynamic modification of string content, making them mutable compared to the immutable nature of regular String objects.

Different Ways to Create String

Several approaches exist for creating a string object in Java, and some commonly used methods are outlined below.

1. Using string literal:This method involves directly assigning a string value to a variable using double quotes.

String str1 = "Hello, World!";

2. Using new keyword: This method employs the new keyword to explicitly instantiate a new string object.

String str2 = new String("Hello, World!");

Java String Methods

Java provides a rich set of methods in the String class to manipulate and work with strings. Here are some commonly used methods:

Method 1: length(): Returns the length (number of characters) of the string.

Example:

class Test {
    public static void main(String[] args) {
        String str = "Hello, World!";
        int length = str.length(); // Returns 13
        System.out.println(length);
    }
}

OUTPUT:

13M

Method 2: charAt(): Returns the character at the specified index.

Example:

class Test {
    public static void main(String[] args) {
        String str = "Hello, World!";
        char firstChar = str.charAt(0); // Returns 'H'
        System.out.println(firstChar);
    }
}

OUTPUT:

H

Method 3:  substring(): Returns a substring within the specified range.

Example:

class Test {
    public static void main(String[] args) {
        String str = "Hello, World!";
        String sub1 = str.substring(7);       // Returns "World!"
        String sub2 = str.substring(0, 5);    // Returns "Hello"
        System.out.println(sub1);
        System.out.println(sub2);
    }
}

OUTPUT:

World!
Hello

Method 4: concat(): Concatenates the specified string to the end of the current string.

Example:

class Test {
    public static void main(String[] args) {
        String str = "Hello, World!";
        String result1 = str.concat(", Java!"); // Returns "Hello, World! Java!"
        String result2 = str + " Java!";        // Returns "Hello, World! Java!"
        System.out.println(result1);
        System.out.println(result2);
    }
}

OUTPUT

Hello, World!, Java!
Hello, World! Java!

Method 5: equals(): Compares the content of two strings for equality.

Example:

class Test {
        String str = "Hello, World!";
        boolean isEqual = str.equals("Hello, World!"); // Returns true
        boolean isEqualIgnoreCase = str.equalsIgnoreCase("hello, world!"); // Returns true
        System.out.println(isEqual);
        System.out.println(isEqualIgnoreCase);
    }
}

OUTPUT:

true
true

Method 6:  indexOf(): Returns the index of the first occurrence of the specified substring.

Example:

class Test {
    public static void main(String[] args) {
        String str = "Hello, World!";
        int indexOfComma = str.indexOf(","); // indexOfComma is 5
        System.out.println(indexOfComma);
    }
}

OUTPUT:

5

Method 7: startsWith(): Checks if the string starts with the specified prefix.

Example:

class Test {
    public static void main(String[] args) {
        String str = "Hello, World!";
        boolean startsWithHello = str.startsWith("Hello"); // startsWithHello is true
        System.out.println(startsWithHello);
    }
}

OUTPUT:

True

Method 8: endsWith(): Checks if the string ends with the specified suffix.

Example:

class Test {
    public static void main(String[] args) {
        String str = "Hello, World!";
        boolean endsWithWorld = str.endsWith("World!"); // endsWithWorld is true
        System.out.println(endsWithWorld);
    }
}

OUTPUT:

True

Conclusion

Overall, the String class is fundamental in Java for text manipulation, and its immutability ensures data integrity.