Java String
String is a sequence of characters which are enclosed in double quotes.
Here is an example of a String variable greeting to which we assign a String literal "Hello, have a nice day!" enclosed in double quotes.
Example
package com.example;
public class StringExample {
public static void main(String[] args) {
String greeting = "Hello, have a nice day!";
System.out.println(greeting);
}
}
Output
String Class
Java also provides the String class to create and manipulate strings. The String class is immutable, which means once it is created, it cannot be changed. A String object can be created by using the new keyword with a constructor.
Here is an example of creating a String object from String class:
package com.example;
public class StringExample {
public static void main(String[] args) {
String stringObject = new String("I am learning Java.");
System.out.println(stringObject);
}
}
Output
Methods in String class
Some of the methods of String class are:
The length() Method
The length() method is used to obtain the number of characters contained in the string object.
Example
package com.example;
public class StringExample {
public static void main(String[] args) {
String message = "The cloud is blue";
int len = message.length();
System.out.println(len);
}
}
Output
Note: Methods which are used to obtain information about an object are known as accessor methods.
The concat() method
The String class provides a concat() method for concatenating two strings:
Example
package com.example;
public class StringExample {
public static void main(String[] args) {
String string1 = "The sky is blue.";
String string2 = "The earth is round.";
String result = string1.concat(" ").concat(string2);
System.out.println(result);
}
}
Output
You can also use the concat() method with string literals as shown below:
"The sky is ".concat("blue");
You can also use the + operator to concatenate Strings in Java.
Example
"Hello," + " world" + "!"
The + operator can also be used to concatenate the end of each line in a multi-line string.
Example
String message = "Do not keep your knowledge to your self " +
"let it travel as far as it can.";
The format() method
The String class has static format() method that allows to create a formatted string which can be reused.
Example
package com.example;
public class StringExample {
public static void main(String[] args) {
float floatValue = 300;
int intValue = 40;
String stringMsg = "Hello world";
String formattedMsg = String.format("The value of the float variable is %f,"
+ " while the value of the integer variable is %d,"
+ " and the string is %s", floatValue, intValue, stringMsg);
System.out.println(formattedMsg);
}
}