What mistake I have done in Interface part of the code?

Question

I am beginner in Java. I know the concept of Interface. Interface is mainly used to achieve full abstraction and to support the functionalities of Multiple Inheritance and then loose coupling.

There can be abstract methods and static constants. It cannot be instantiated and similar like Abstract class. Interface is a blueprint of a class and it represents Is-A-Relationship.

I myself just tried this sample program:

interface Printable{
void print();
}
public class A implements Printable{
public void Print(){
 System.out.println("Prints..");
}
public static void main(String args[]){
 A obj=new A();
 obj.print();
}
}

Output is,

Compiling the source code....
$javac A.java 2>&1
A.java:4: error: A is not abstract and does not override abstract method print() in Printable
public class A implements Printable{
^
A.java:10: error: cannot find symbol
obj.print();
^
symbol: method print()
location: variable obj of type A
2 errors

What does it mean by "A is not abstract and cannot override abstract method print()"?

What mistake I have done here? So I can learn from my mistakes!

• DGomez: Print method should be in lower case
• Maroun: Java is case sensitive. Print and print are not the same.
• Jorge Campos: @DGomez you should post as answer shouwing an example.
• scottb: "Interface is a blueprint of a class and it represents Is-A-Relationship." This is incorrect. If a type has a strong "is a" relationship with an existing class, then that is the right time to be thinking about inheritance. Interfaces are used to express a common contract that can be shared by classes even if they are not related by hierarchy. For interfaces, the contract is the thing ... and no "is a" relationship is required.
• Achiever: @scottb So, it means Interface indicates the common contract so that can share the abstract methods by any other classes?

Answer 1

void print()

vs

void Print()

It's a capital mistake.

You are getting the error

A is not abstract and does not override abstract method print()

Because abstract classes can implement an interface without actually implementing the methods it defines.

See here:

In the section on Interfaces, it was noted that a class that implements an interface must implement all of the interface's methods. It is possible, however, to define a class that does not implement all of the interface methods, provided that the class is declared to be abstract.

The other part of the error message is from the above "capital" mistake.

• Achiever: Oh I am sorry, this minor mistake I have not found it. Thanks !
• Achiever: I referred the link which you have mentioned. What does it mean and how does it looks?"When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class. However, if it does not, the subclass must also be declared abstract."
• Jeroen Vannevel: What is unclear to you? It's exactly as it says there: the eventual subclass that you want to instantiate must implement all interface methods and all abstract methods. These can be implemented in superclass during the chain, but if there are any abstract methods or unimplemented methods left, you'll have to make the class abstract and provide another subclass that does implement them.

Answer 2

The error is very clear

A.java:4: error: A is not abstract and does not override abstract method **print()** in Printable

As you see the method is print() not Print()

Answer 3

please check your spell of Print(). it is in lowercase in interface