String variables in static method

[vidhya suvarna]

Source:
]http://www.javabeat.net/javabeat/scjp2/mocks/scjp_1_4_mock_exam_questions_2.php

public class Test14{
static String s ="Instance";
public static void method(String s){
s+="Add";
}
public static void main(String a[]){
Test14 t = new Test14();
s = "New Instance";
String s = "Local";
method(s);
System.out.println(s);
System.out.println(t.s);
}
}
What is output?
A1 Local Instance
A2 Local New Instance
A3 Loca Add New Instance
A4 Compiler Error

The correct ans is Local New Instance.

Can someone tell me why the value of s updated in method() doesnt affect it when it's displayed?

[ September 17, 2008: Message edited by: vidhya suvarna ]
[ September 17, 2008: Message edited by: vidhya suvarna ]

[sannuth kashikar]

public class Test14{
static String s ="Instance";              //s is a static variable
public static void method(String s){     //s is a local to method 
s+="Add";                                //concat with the method parameter
}
public static void main(String a[]){
Test14 t = new Test14();
s = "New Instance";    //changing static variable to refer to
                          // "new instance " object.   
String s = "Local";    // local variable 
method(s);    //not effect since"method()" is not changing static variable  
System.out.println(s); //print local variable "Local".here s is reffering to local
System.out.println(t.s);//here u can use with the class name "Test14.s" or 
                        //refernce type "t.s" to refer to static variable s 
                        //which is reffering  to the objet "New Instance"
}
}
 
Hence the output :Local
                  New Instance

[chander shivdasani]

public class Test14{
static String s ="Instance";
public static void method(String s){
s+="Add";
}
public static void main(String a[]){
Test14 t = new Test14();
public class Test14{
static String s ="Instance";
public static void method(String s){
s+="Add";
}
public static void main(String a[]){
Test14 t = new Test14();
s = "New Instance";
String s = "Local";
method(s);
System.out.println(s);
System.out.println(t.s);
}
}
}
}

In these kind of questions, just remember that local variables have priority over other variables.

s = "New Instance";//This is Static variable

String s = "Local";//This is local variable

method(s); //Local variable take precedence over static, so local variable is sent to the function.

and the function modifies the local variable(The variable local to this function)

[vidhya suvarna]

If you change the occurrence of statements:
s = "New Instance";
String s = "Local";

as

String s = "Local";
s = "New Instance";

you will find that static variable is passed to the method.

My query is s is a String variable(object) so if we update its value in a method wouldnt it be reflected when it returns from the method?

[Stephen Davies]

Here is my take on things.

public class Test14 {

static String s ="Instance"; // all instances of this class will have this member variable

public static void method(String s){

s+="Add";
}

//so far to here s="Instance"

public static void main(String a[]){
Test14 t = new Test14(); // s ="Instance"
s = "New Instance"; // static variable s is now ="New Instance" (static changed for Test14 class")
String s = "Local"; // new Local variable s = "Local" 
method(s); // essentially does nothing to the original string you are passing a[B] copy of Local s[/B]

System.out.println(s);// Local variable s ("Local")
System.out.println(t.s); // main class Test14 static variable s ("New Instance");
}

 
}

[ September 17, 2008: Message edited by: Stephen Davies ]

[vidhya suvarna]

Thanks Stephen i got it now!