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

Signature of toUppercase()

public String toUpperCase()

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

Note

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

Calling toUpperCase() method on a String object.




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


class StringUpper
{
public static void main(String[] ar)
{
String str= new String("new zealand");
System.out.println("Original String is : "+ str);
System.out.println("String's upper case value : " + str.toUpperCase());
}

}





Output




String's value : new zealand
String's upper case value : NEW ZEALAND


A String object was initialized to a value new zealand. When the method toUpperCase() was called on this String object, it returned the content of the invoked String in upper case letters.






Method toUpperCase() does not modify the original content in a String object


The method toUpperCase() only returns the content of String object in upper 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 upper case all the characters in it by calling toUpperCase() method on this String object.

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


class StringUpper
{
public static void main(String[] ar)
{
String str= new String("mars - the red planet");
System.out.println("Original String is : "+ str);
System.out.println("String's upper case value : " + str.toUpperCase());

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

}





Output is :




String's value : mars - the red planet
String's upper case value : MARS - THE RED PLANET
String's value : mars - the red planet


Even after calling the method toUpperCase() on the String object, the original case of its content remains the same - mars - the red planet, because the method toUpperCase() only returns the upper 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 toUpperCase() method on the original object, we can make the reference variable to the original string, point to the result of calling the toUpperCase() method(but in this case, the original string will be lost).



//Program to convert a string to Uppercase letters. 

class StringUpper2
{
public static void main(String[] ar)
{
String str = new String("hurray! it's sunday!");
System.out.println("Original string is : "+ str);

str = str.toUpperCase(); //result of calling the toUpperCase() method

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





Output is :




Original string is : hurray! it's sunday!
String's value after converting to upper case : HURRAY! IT'S SUNDAY!








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