Cannot find symbol - class T

Question

I've this function;

  public static T[] addToArray(T item, T... items){
    T[] array;
    int array_size = 1;

    if(items !=null){ array_size = items.length+1; }

    array = java.util.Arrays.copyOf(items, array_size);
    array[array_size-1] = item;

    return array;
  }

And I get this error cannot find symbol symbol: class T. The idea is to make this method generic. I never worked with generics so I'm guessing I miss some reference?

Solution 1

Method signature for generic method is as follows

 public static <T> T[] addToArray(T item, T... items){
      T[] array;
      int array_size = 1;

      if(items !=null){ array_size = items.length+1; }

      array = java.util.Arrays.copyOf(items, array_size);
      array[array_size-1] = item;

      return array;
    }

Solution 2

You need to declare the type parameter before the return type of the method:

public static <T> T[] addToArray(T item, T... items)

Reference:

• Java Generics FAQs
  • What is a generic method?
• Oracle Tutorial

Solution 3

To make a generic method, you need to declare it as taking a generic type parameter:

public static <T> T[] addToArray(...)

Comments

[maba]

I think it's better to link to the official tutorial instead: docs.oracle.com/javase/tutorial/extra/generics/methods.html

[Rohit Jain]

@maba. Well, I've linked the best reference I know about generics. Anyways, official one is also worth reading.

[Ermiya Eskandary]

Why though? Just spent 15 minutes trying to figure out how to do this coming from a C# background - if the compiler can see T, why do we need the type parameter...