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The toLowerCase() method of String class is used to convert all the characters in a String to lower case letters.

Signature of toLowercase()

public String toLowerCase()

• Access modifier - toLowerCase() method is a public method.
• Parameter passed - No value is passed to it.
• Value returned - It returns the lower case String value of a String object on which toLowerCase() method was called.

Note

Method toLowerCase() method when called on any String object, returns its contents as an lower case String. The returned lower case String must be stored or used otherwise it is lost.

Calling toLowerCase() method on a String object.




//Program to convert a String to lower case letters. 


class StringUpper
{
public static void main(String[] ar)
{
String str= new String("HELLO	, HOW ARE YOU?");
System.out.println("Original String is : "+ str);
System.out.println("String's lower case value : " + str.toLowerCase());
}

}





Output is :




String's value : HELLO, HOW ARE YOU?
String's lower case value : hello, how are you?


A String object was initialized to a value HELLO, HOW ARE YOU?. When the method toLowerCase() was called on this String object, it returned the content of the invoked String in lower case letters.






Method toLowerCase() does not modify the content in a String.


The method toLowerCase() only returns the content of String object in lower case letters without modifying its original content at all.


Let's understand this by an example -:
Here in program below, we have initialized a String object with a value new york and we are trying to lower case all the characters in it by calling toLowerCase() method on this String object.

//Program to convert a String to lower case letters. 


class StringUpper
{
public static void main(String[] ar)
{
String str= new String("HURRAY! It's Sunday!");
System.out.println("Original String is : "+ str);
System.out.println("String's lower case value : " + str.toLowerCase());

System.out.println("String value : " + str);
}

}





Output is :




String's value : HURRAY! It's Sunday!
String's lower case value : hurray! it's sunday!
String's value : HURRAY! It's Sunday!


The String object value remains the same - HURRAY! It's Sunday!, even after the method toLowerCase() was called on it, because the method toLowerCase() only returns the lower case form of the content in a String object, without changing the original case of its content.




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Strings are immutable but reference variables are mutable.


String objects are immutable, but the reference variables pointing to them are not, therefore in order to display the result of calling the toLowerCase() method on the original object, we can make the reference variable to the original string, point to the result of calling the toLowerCase() method(but in this case, the original string will be lost).



//Program to convert a string to lower case letters. 

class StringUpper2
{
public static void main(String[] ar)
{
String str= new String("CZECH REPUBLIC");
System.out.println("Original string is : "+ str);

str=str.toLowerCase(); //result of calling toLowerCase() is stored back in String object

System.out.println("String's value after converting to lower case : " + str);
}
}

Output is :

Original string is : CZECH REPUBLIC
String's value after converting to lower case : czech republic








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