Strings, I/O and formatting (Part-1)

"Hey Isla Are you serious??Strings,IO and formatting???"Hmmm..yeah I agree with you.This is basic Java.Anyway no problem we'll go further and discuss and see how much you know about Java Strings,I/O and formatting.We'll start with a little background information about strings.

• Strings are immutable objects.(You know what I mean)
• String is a 16-bit Unicode character
• In java string is an object.You can create a new instance using new keyword

String myString=new String();

This creates a new string object and assign it to myString reference variable.Cool..Now we need to assign a value to the new variable.Let's do it like this.

myString="Hasitha";

And we are done.Now we have a string variable with a value.Is this the only way we can do this.Absolutely no.String class has a number of constructors.We can do the same thing as follows.

String myString=new String("Hasitha");
String myString="Hasitha";

Hmmm...Note that there are some differences between these options.We'll discuss those later.Now you know how to instantiate a string variable and assign a value to it.Okay now we'll move to the following example.

String s=myString;

We instantiated a new variable which is referring to the same myString reference.

myString=myString.replace("tha","");
System.out.print(myString+",");
System.out.println(s);

So according to you what would be the output.A simple question.Obviously it's Hasi,Hasi.Since s is referred to the same myString reference,when myString changes s should change.But you are wrong.The output is Hasi,Hasitha.WTH....!!!!. Yeah that's the beauty of immutability in Java strings.Once you created a string object it remains the same throughout the program until you re- instantiate it.So what is happening here.

• A new String object is created in the heap with the reference myString and the value Hasitha
• The same object is referenced by s.
• When myString.replace invokes it creates a new object in heap and assign myString reference to that new object
• S is still referring to the original Hasitha :p string.

The immutability of strings can illustrate further by following example.

String s="I am don";
s.replace("don","hasitha");
System.out.println(s);

As we learned this prints "I am don" in console.So that's it we have learned some interesting facts about strings in Java in this post.Let's talk more about Strings in next post.