Java Generics
Generics introduce type parameters to Java code. For example:
Generics are important because:
List<String> names = new ArrayList<>();
Here, String is the type parameter for the generic class List<T>. The T is a placeholder that gets replaced with a real type (like String, Integer, etc.) when the code is compiled.- Type safety - Catch type errors at compile time.
- Code reusability - Write a method/class once and use it for different types.
- Elimination of casts - No need to manually cast when retrieving objects.
- Cleaner code - More readable and maintainable.
class Gen<T>{
T val;
Gen(T v){
val = v;
}
T getVal(){
return val;
}
void showType(){
System.out.println("Type: "+val.getClass().getName());
}
}
Bounded Generics, here T is of type Number
Here, Generics class can of any Number type like: Integer, Float, Double, Long etc.
class Gen_ii<T extends Number>{
T[] val;
Gen_ii(T[] values){
val = values;
}
void sum(){
double sum = 0;
for(int i=0;i<val.length;i++)
sum += val[i].doubleValue();
System.out.println("Sum: "+sum);
}
}
class Generics_demo{
public static void main(String[] arrgs){
Gen<Integer> g = new Gen<Integer>(77);
int x = g.getVal();
System.out.println("x: "+x);
g.showType();
Integer[] list = {1,2,3,4,5,6,7,8,9,10};
Gen_ii<Integer> gg = new Gen_ii<Integer>(list);
gg.sum();
Double[] dlist = {1.2,2.4,4.5};
Gen_ii<Double> dg = new Gen_ii<Double>(dlist);
dg.sum();
}
}