Athira Vineeth

Make a class immutable by following these guidelines :

ensure the class cannot be overridden - make the class final, or use static factories and keep constructors private
make fields private and final
force callers to construct an object completely in a single step, instead of using a no-argument constructor combined with subsequent calls to setXXX methods (that is, avoid the Java Beans convention)
do not provide any methods which can change the state of the object in any way - not just setXXX methods, but any method which can change state
if the class has any mutable object fields, then they must be defensively copied when passed between the class and its caller
For more details refer this link

http://www.javapractices.com/topic/TopicAction.do?Id=29


Thanks,
Athira

Hi

I have two class A and B, where B extends A.
public class ClassA { public void printMe(){ System.out.println("Inside A"); } }
public class ClassB extends ClassA{ public void printMe(){ System.out.println("Inside B:Print Me"); } public void printMy(){ System.out.println("Inside B :Print My"); } }

Main class

public class ClassMain { public static void main(String args[]){ ClassA a=new ClassB(); a.printMe(); } }

In this case it will print" Inside B:Print Me"
That means Object a of reference ClassA has access to the method defined inside ClassB.

But if i call a.printMy();then it is showing compilation error.
Why so?

Thanks in Advance
Athira

hi

try this
[Moderator action: Removed ready-made solution. Athira Vineeth, please DontBeACodeMill.(⇐click)]

Hi

Hope this will work
package xyz; public class z implements x{ y y1=new y(); geta(){ return y1.geta1(); } getb(){ return y1.getb1(); } }

yes its help me a lot.

thank you so much for your time.

Hi

in the below example
public class OverLoadTest { public static void main(String[] args) { OverLoadTest overLoadTest=new OverLoadTest(); overLoadTest.printValue(null); } public void printValue(Object ob){ System.out.println("Object"); } public void printValue(String ob){ System.out.println("String"); } }

The output of this program is "String".
Why so?Why it is not executing the printValue(Object ob) method?

Thank you!!

To compare two objects for equality you can override equals method.

Thanks
Athira

Hi

In java it is not possible to instantiate an abstract class. Then why there need a constructor inside abstract class?

Thanks in Advance
Athira

Thanks Brown!!

that link is very helpful.

it is clear now
From this example
class Super { static String greeting() { return "Goodnight"; } String name() { return "Richard"; } } class Sub extends Super { static String greeting() { return "Hello"; } String name() { return "Dick"; } } class Test { public static void main(String[] args) { Super s = new Sub(); System.out.println(s.greeting() + ", " + s.name()); } }
output is Goodnight, Dick

Thanks
Athira

In a class hierachy, when a method in a subclass has the same name and type signature as a method in its super class, then a method in the subclass is said to override the method in the super class.
When an overriden method is called from within a subclass, it will always refer to the version of that method defined by the subclass.The version of the method defined by the superclass will be hidden.

In that sense main method is said to be overriding.right?

hi

i think it is because
if(locationCells.isEmpty()){ // once the arraylist is empty the entity has sunk result="kill"; } else{ // else mark a hit! result="hit"; }

locationCells is not empty so it is always printing hit. in the first code

after changing the if(index>=0) position ,the execution never entered into if(index>=0){ block

so the default value got printed "miss"

Thanks for the reply.

But still i am in confusion

i have a class called MainClass
public class MyMainClass { public static void main(String[] args) { System.out.println("my main method"); } }

one subclass called that xtend main class

public class OverridingMain extends MyMainClass{ public static void main(String[] args) { System.out.println("main got overriden"); } }

here the signature of main method is same that means main method got overriden .right?

Hi

Is it possible to override main method?

Thanks in Advance
Athira

Hi,

intern() method
Returns a canonical representation for the string object.
A pool of strings, initially empty, is maintained privately by the class String.

When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the equals(Object) method, then the string from the pool is returned. Otherwise, this String object is added to the pool and a reference to this String object is returned.

It follows that for any two strings s and t, s.intern() == t.intern() is true if and only if s.equals(t) is true.

For example

try this
String str="abc"; String str2=new String("abc"); System.out.println(str==str2);

this will output false

try this
String str="abc"; String str2=new String("abc"); System.out.println(str==str2.intern());

this will output true