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- String represents a group of character.
- In java, string is an object of String class in java.lang package but in C language, it is an array of characters in which the last character is ‘\0’.
- Java has character array too but String is a class. String is also a data type since a class is also called user defined data type.
Syntax :
| String welcome = “hello”; |
where, ‘welcome’ is a variable to store the data which is of type ‘String’. Thus a group of characters is assigned to the variable ‘welcome’ . As already mentioned, String is a class, therefore an object of type String is created and referenced by a variable ‘welcome’.
We have another way of creating String by using new operator as
| String welcome = new String(“hello”); |
The string ‘hello’ is assigned to the String variable ‘welcome’.
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public class StringExample { public static void main(String args[]) { char arr[] = { 'h', 'e', 'l', 'l', 'o'}; String welcome = new String(arr); System.out.println( welcome ); } } |
This would produce following result:
Output:
| Hello |
Note: String class is made ‘final’ class. Strings are constant which means, their values cannot be changed once they are created.
String Class Methods:
int length(): To find the length of a string.
s.length(); gives the length of string s.
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import java.lang.*; import java.io.*; public class StringLengthExample{ public static void main(String[] args) throws IOException{ BufferedReader bf = new BufferedReader(new InputStreamReader(System.in)); System.out.println("Enter a string to find its length: "); String s = bf.readLine(); int length = s.length(); System.out.println("length of string is : " + length); } } |
Output:
| C:\> javac StringLengthExample.java C:\> java StringLengthExample Enter a string to find its length: Hello length of string is : 5 |
String concat(String s): To concatenate or join two strings.
String s3 = s1.concat(s2); String s1 and s2 are concatenated or joined and the resulting String is stored in String object s3.
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import java.io.*; public class StringConcatExample{ public static void main(String[] args) throws IOException{ BufferedReader bf = new BufferedReader(new InputStreamReader(System.in)); System.out.println("Enter Your First String:"); String s1 = bf.readLine(); System.out.println("Enter Your Second String:"); String s2 = bf.readLine(); String s3 = s1.concat(s2); System.out.println("Concatenated string is: " + s3); } } |
Output:
| C:\> javac StringConcatExample.java C:\> java StringConcatExample Enter Your First String: Hello Enter Your Second String: World Concatenated string is: HelloWorld |
Pls refer the below link to explore more String methods.
http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#method_detail
Strings are immutable:
Strings are immutabe which means, their value cannot be changed once they are created. But if we try to modify the contents of a String object, then the JVM will modify the content and store it in a new object instead of the original object. The original object will remain unmodified.
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public class StringExample { public static void main(String args[]) { String s = "XYZ"; s = s.toLowerCase(); System.out.println( s ); } } |
Output:
| xyz |
When you see the output of the program, it looks like the String s is modified. But what happened is that the original object remains unchanged and a new object is created with the modified data during its construction and the variable s refers to the newly created object.
But there are some conditions where we will need mutable Strings and is achieved by StringBuffer which we will discuss in the next chapter.