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Following is the one part of Java Course. – Working of String
According to Oracle String in Java are sequence of
characters and are represented by a class java.lang.String.
So in simple words String in Java are objects.
Declaration for String class looks like this
public final class String extends Object
String in Java are of nature Immutable as they are declared
as final.
String can be declared in multiple ways in java
For example
String str="Java";
In this case str is a String literal as it is declared
directly using = sign.
While execution JVM creates a String object and store it in
Object Heap.
Other way of Declaration
String s=new String("Hello");
or
char[] charArray=new char[]{'s','u','c','c','e','s','s'};
String s1=new String(charArray);
An important concept which many people don't take notice of
is the following situation.
String str="java";
str=str.concat("withz.in");
System.out.println(str);
String is of nature final and final objects can change their
reference.
So what happens when we print this and how many String
objects are created in this process.
On the very first line.
String str="java";
JVM created a new object with value "java".
When we concat other String "withz.in" in the
original String str.
But as String is of nature final it cannot make changes in
the same object reference, hence it first creates a new object
"withz.in" and then concat the other two Strings and create a new
String "javawithz.in" and we have used assignment operator
str=str.concat("withz.in");
Now str points at the third object created and first two
objects lies unidentified in Heap and when we print we print it we get output
as "javawithz.in"
Now let us take another example for understanding the same
concept
String str="java";
str.toUpperCase();
System.out.println(str);
Now in this case when the first line got executed JVM
created a new String object "java" and str was pointing at the same
object.
Then we did
str.toUpperCase();
This created a new Object with value "JAVA" but as
we haven't used any assignment operator str is still pointing at old reference
and not the new.
So when we print it we will get "java".
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