Why can't Java generics be used for static methods?


Generics is a concept in Java where you can enable a class, interface and, method, accept all (reference) types as parameters. In other words it is the concept which enables the users to choose the reference type that a method, constructor of a class accepts, dynamically. By defining a class as generic you are making it type-safe i.e. it can act up on any datatype.

Generics for static methods

We can use generics for static methods

 Live Demo

public class GenericMethod {
   static <T>void sampleMethod(T[] array) {
      for(int i=0; i<array.length; i++) {
         System.out.println(array[i]);
      }
   }
   public static void main(String args[]) {
      GenericMethod obj = new GenericMethod();
      Integer intArray[] = {45, 26, 89, 96};
      sampleMethod(intArray);
      String stringArray[] = {"Krishna", "Raju", "Seema", "Geeta"};
      sampleMethod(stringArray);
      Character charArray[] = {'a', 's', 'w', 't'};
      sampleMethod(charArray);
   }
}

Output

45
26
89
96
Krishna
Raju
Seema
Geeta
a
s
w
t

What we can’t use is static before the type parameters of generic class.

Example

 Live Demo

class Student<T>{
   static T age;
   Student(T age){
      this.age = age;
   }
   public void display() {
      System.out.println("Value of age: "+this.age);
   }
}
public class GenericsExample {
   public static void main(String args[]) {
      Student<Float> std1 = new Student<Float>(25.5f);
      std1.display();
   }
}

Compile time error

GenericsExample.java:3: error: non-static type variable T cannot be referenced from a static context
      static T age;
            ^
1 error
raja
Published on 09-Sep-2019 11:12:47
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