In Java, a string is a sequence of characters that represents a text-based data. The String class is part of the Java core library and is used to create and manipulate strings.
Strings in Java are immutable, which means that once a string is created, its value cannot be changed. This is different from other types of variables in Java, which can be modified.
To create a string in Java, you can use either a string literal or a String object. A string literal is a sequence of characters enclosed in double quotes, while a String object is created using the new keyword followed by the String class name and a set of parentheses.
For example:
String s1 = "Hello, World!"; // string literal
String s2 = new String("Hello, World!"); // String object
Java provides a number of methods to manipulate strings, such as concatenation, substring, length, and so on. Strings can be concatenated using the + operator, or the concat method, and substrings can be extracted using the substring method.
String s1 = "Hello, ";
String s2 = "World!";
String s3 = s1 + s2; // concatenation using the + operator
String s4 = s1.concat(s2); // concatenation using the concat method
System.out.println(s3); // prints "Hello, World!"
System.out.println(s4); // prints "Hello, World!"
Overall, strings are an essential part of Java programming and are used extensively in various applications, from simple console-based programs to large enterprise-level applications.