Java Basics Using Qt Jambi Tutorial

Generics

Generics makes it easy to catch runtime bugs such as wrong argument types. It tells the compiler to inform an error when there are wrong types, when a method call passes a string when it is expecting an integer.

Ex.

public class Vehicle{

private Object object;

public void start(Object object){

this.object = object;

}

public Object speed(){

return object;

}

public static void main (String[] args){

Vehicle v1 = new Vehicle(); created by different programmer

vi.start(“100”);

Integer speedofv = (Integer)v1.speed();

System.out.println(“speed of car is “ + speedofv);

}

} created by another programmer

This will result an error because it passes string where it expects an integer (this is at runtime not compile time).

Example on how to use generics:

public class Vehicle{

private T t; //T stands for type

public void start(T t){

this.t = t;

}

public T speed(){

return t;

}

//we just replaced Object with T.

public static void main(String[] args){

Vehiclev1 = new Vehicle();

v1.start(“100”);

Integer speedofv = v1.speed(); //no explicit casting

System.out.println(speedofv);

This will result an error in compile time having wrong types.

Type Convention:

1. T-type

2. N-Number

3. E-Element

4. V-Value

5. K-Key

You can also use generics in methods. The difference is it only accessed inside the method.

public<u>void direction(U u){

System.out.println(“T:” + t.getClass().getName());

System.out.println(“U:” + u.getClass().getName());

}

public static void main (String[] args){

Vehicle<integer>v1 = new Vehicle();

v1.start(100);

v1.speed();

v1.direction(“North”);

}

prints out: T: java.lang.Integer

U:java.lang.String

to be continued...