Strings in Java

 A string is a sequence of characters surrounded by double quotations. In a java programming language, a string is the object of a built-in class String.

In the background, the string values are organized as an array of a character data type.

The string created using a character array can not be extended. It does not allow to append more characters after its definition, but it can be modified.

Example

char[] name = {'J', 'a', 'v', 'a', ' ', 'T', 'u', 't', 'o', 'r', 'i', 'a', 'l', 's'};

//name[14] = '@';            //ArrayIndexOutOfBoundsException

name[5] = '-';

System.out.println(name);

 

The String class defined in the package java.lang package and is immutable, meaning once a string object is created, it cannot be changed.

Creating String object in java

In java, we can use the following two ways to create a string object.

• Using string literal
• Using String constructor

 

String title = "Java Tutorials";     // Using literals                          

String siteName = new String("www.mybcaclassnotes.blogspot.com");      // Using constructor

 

In Java, String handling is supported by many built-in methods in the String class.

1. length()

Returns the number of characters in the string.

String str = "Hello";

System.out.println(str.length());  // Output: 5

2. charAt(int index)

Returns the character at the specified index (0-based).

String str = "Java";

System.out.println(str.charAt(2));  // Output: v

3.  substring(int beginIndex) and substring(int beginIndex, int endIndex)

Returns a part of the string.

String str = "Programming";

System.out.println(str.substring(3));      // Output: gramming

System.out.println(str.substring(3, 7));   // Output: gram

4. equals(String anotherString)

Checks if two strings are exactly equal (case-sensitive).

String s1 = "Hello";

String s2 = "hello";

System.out.println(s1.equals(s2));  // Output: false

5. equalsIgnoreCase(String anotherString)

Checks equality, ignoring case.

String s1 = "Hello";

String s2 = "hello";

System.out.println(s1.equalsIgnoreCase(s2));  // Output: true

6. toUpperCase() and toLowerCase()

String name = "Prasanjeet";

System.out.println(name.toUpperCase());  // Output: PRASANJEET

System.out.println(name.toLowerCase());  // Output: prasanjeet

7. concat(String str)

Appends the specified string to the end.

String s1 = "Hello";

String s2 = "World";

System.out.println(s1.concat(" " + s2));  // Output: Hello World

8. replace(char oldChar, char newChar)

Replaces characters in a string.

String str = "apple";

System.out.println(str.replace('p', 'b'));  // Output: abble

9. trim()

Removes whitespace from the beginning and end.

String s = "  Java  ";

System.out.println(s.trim());  // Output: Java

10. contains(CharSequence s)

Checks if a string contains a sequence.

String str = "I love Java";

System.out.println(str.contains("love"));  // Output: true

11. startsWith(String prefix) and endsWith(String suffix)

String str = "filename.txt";

System.out.println(str.startsWith("file"));  // Output: true

System.out.println(str.endsWith(".txt"));    // Output: true

12. indexOf(char ch) and lastIndexOf(char ch)

Returns the index of the first/last occurrence of the character.

String str = "banana";

System.out.println(str.indexOf('a'));      // Output: 1

System.out.println(str.lastIndexOf('a'));  // Output: 5