Question

2. In java, String is an immutable object which means it is constant and can cannot be changed once it has been created. (5 marks) • Demonstrate your understanding of String. Provide two ways to define a String in java, support your answer with examples. •

Answer 1

1)

String Immutability is an important concepts in Java. English meaning "Immutable" is fixed/unchangeable.

Lets us understand with a simple example.

Lets declare a string

 String str = "Old Java"

and change the content of the string as

 str = "New Java"

and if we print the string then we would get the latest string rather than the old one.

public class Demo { public static void main(String[] args) { String str = "Old Java"; str = "New Java"; System.out.println(str); } } Demo > main Demo /usr/lib/jvm/java-8-openjdk-amd64/bin/java New Java

From the above output we can see. The string is obtained new value.

Then, the string immutability is the concept that comes when the JVM is allocating the strings in its heap memory.

To understand lets see one more example.

public class Demo { public static void main(String[] args) { String str = "Old Java"; str.concat(" is obselete"); System.out.println(str); } } Demo > main() Demox /usr/lib/jvm/java-8-openjdk-amd64/bin/java old Java

An important point to note here is that, while the String object is immutable, its reference variable is not.  So that’s why, in the above example, the reference was made to refer to a newly formed String object.

The old string would still be there in the JVM's Sring constant pool but the reference variable is put with the new value in case of the first example. Whereas in the second example, the string has been concatenated with another string but that is not stored anywhere in any string variable hence the concatenated value is replicated in the original string variable.

Please refer the below example:

public class Demo { public static void main(String[] args) { String str = "old Java"; String newStr = str.concat(" is Obselete"); System.out.println(newStr); } } Demo Demox /usr/lib/jvm/java-8-openjdk-amd64/bin/java ... Old Java is Obselete

2)

As we are aware of it, String in Java is special data type that acts as primitive and non-primitive manner.

A primitive way to define String

 String str = "Old Java";

Non-primitive way (String as object)

 String str = new String("New Java");

With respect to Strings the first way will store the string in String Constant Pool and second way would store in normal heap of JVM