Question

I am wondering do we use generic method only if the method is static ? for non-static you would define a generic class and you don’t necessary need it to be generic method. Is that correct ?

for example,

  public class Example<E>{

         //this is suffice with no compiler error
         public void doSomething(E [] arr){
                for(E item : arr){
                    System.out.println(item);
                }
         }

         //this wouldn't be wrong, but is it necessary ?
         public <E> doSomething(E [] arr){
                for(E item : arr){
                    System.out.println(item);
                }
         }
  }

whereas the compiler will force to add type parameter to make it a generic method if it’s static.

  public static <E> doSomething(E [] arr){


  }

I am not sure if i am correct or not.

Answer 1

public class Example<E>{

defines a generic type for instance’s methods and fields.

public void <E> doSomething(E [] arr){

This defines a second E which is different to the first and is likely to be confusing.

Note: void is still needed 😉

Static fields and methods do not use the generic types of the class.

public static <F> doSomething(F [] arr) { }

private static final List<E> list = new ArrayList<>(); // will not compile.