The most important part of your life

The most important part of your life is the time you spent with these people (other people of the flight).

- Lost

We can't let other people decide who you are

We can't let other people decide who you are dude
you have to decide that for yourself
-Lost

Superiority should be such a big burden to carry

When one feels superior to others, there is a urge to produce better results than others. Results are not in one's control, effort is. When results are not forth coming for oneself, when it is for others, it can run contradictory to one's superiority beliefs. Then superiority should be such a big burden to carry.

Java Generics - Part 1

Generics were introduced in JDK 5.0. Generics help write re-usable code without losing type safety. Type safety helps write robust programs. The most common usage of generics is in the collections API.

 

Prior to generics, a Collection could theoretically hold values of various types. Like so:

 

import java.util.Collection;

import java.util.LinkedList;

class Generics1

{

       public static void main(String[] args)

       {

              Collection nameList = new LinkedList();              

              nameList.add( new Integer(0) ); // 1 Integer added to collection

              nameList.add( "test" );         // 2 String added to collection

              System.out.println( nameList );

       }

}

 

Compiling the above code with JDK 5.0 and above will result in a “warning”. But the class file does get generated. Like so:

 

$ javac Generics1.java

Note: Generics1.java uses unchecked or unsafe operations.

Note: Recompile with -Xlint:unchecked for details.

 

Running the class file does give the following output:

 

$ java Generics1

[0, test]

 

But now we have a Collection with a Integer and a String. Its highly un-likely that a programmer would expect to see a Integer in a nameList.

 

To enforce type safety that the nameList can only hold String instances, change the declaration of nameList like so:

 

import java.util.Collection;

import java.util.LinkedList;

class Generics1

{

       public static void main(String[] args)

       {

              Collection<String> nameList = new LinkedList<String>();

              nameList.add( new Integer(0) ); // Violation (Integer added to String collection) caught by compiler.

              nameList.add( "test" );        

              System.out.println( nameList );

       }

}

 

 

Now, the compiler checks each operation on the Collection and ensures that only Strings find place in the Collection (type correctness). Compilation fails if there are violations (like above):

 

$ javac Generics1.java

Generics1.java:8: add(java.lang.String) in java.util.Collection<java.lang.String> cannot be applied to (java.lang.Integer)

                nameList.add( new Integer(0) );

                        ^

1 error

 

Since all Collection elements are held as java.lang.Object in a non-generic Collection, all fetches must be cast to the appropriate type. Failing to do so will result in a compilation failure. Like so:

 

import java.util.List;

import java.util.LinkedList;

class Generics1

{

       public static void main(String[] args)

       {

              List nameList = new LinkedList();

              nameList.add( "test" );

              String firstName = nameList.get(0);

System.out.println( firstName );

       }

}

 

$ javac Generics1.java

Generics1.java:9: incompatible types

found   : java.lang.Object

required: java.lang.String

                String firstName = nameList.get(0);

                                               ^

Note: Generics1.java uses unchecked or unsafe operations.

Note: Recompile with -Xlint:unchecked for details.

1 error

 

This issue can be resolved by explicitly casting the assignment or typing the collection with generics like so:

 

              List<String> nameList = new LinkedList<String>();

 

$ java Generics1

Test

 

In the above case, List is a generic interface with a type parameter.