Behavior of Object reference when assigned to null and ""

Difference between assigning String reference to null or empty quotes

Instance variables are initialized to a default value each time a new instance is created

But String and other Object references are assigned to null by default.Its always a good practice to assign a value explicitly to variables which increases code readability.

Lets see what happens when we invoke String related methods when String reference is assigned to null or "".

Program 1 :-

public class StringReference {

/**

* @param args

*/

String str1;

public String getStr1() {

return str1;

}

public static void main(String[] args) {

// TODO Auto-generated method stub

StringReference sr = new StringReference();

String strl = sr.getStr1();

System.out.println(strl.length());

}

}

Run the above program it throws nullpointer exception because str1 is a reference and is not pointed to any object. So invoking a reference which doesnt point to an Object will throw null pointer exception.

Output :-

Exception in thread "main" java.lang.NullPointerException

at StringReference.main(StringReference.java:16)

Now lets see assigning String variable to ""

public class StringReference {

/**

* @param args

*/

String str1="";

public String getStr1() {

return str1;

}

public static void main(String[] args) {

// TODO Auto-generated method stub

StringReference sr = new StringReference();

String strl = sr.getStr1();

System.out.println(strl.length());

}

}

Output :- 0

Here Str1="" creates an empty String object

Now Str1 is referring to an object so invoking String related methods liketoUpperCase(),length() etc. will not throw null pointer exception.

Happy Learning

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