CODEWITHSUNDEEP
javaobjectreturn
Raggaer
Raggaer

Reputation: 3318

Java returning an Object

Im currently learning Java and Im now facing the following error

Object label1 = addLabel("First number");

And my addLabel function

public Object addLabel(String text)
{
     JLabel label = new JLabel(text);
     add(label);

     return label;
}

I was wondering why I cant access any of the methods of label on my variable label1 if Im returining it as an object?

Ex : label1.setBounds(...);

Upvotes: 3

Views: 155

Answers (3)

Jason
Jason

Reputation: 11832

There's a difference between the type of object that exists in memory, and the type of reference you have to it.

In this case, your object in memory is a JLabel, but your reference is an Object - so code using this reference can only see methods available in Object.

If you chose to return your object as a JLabel and store the reference as a JLabel, your subsequent code would have access to the methods in JLabel.

Upvotes: 0

Hovercraft Full Of Eels
Hovercraft Full Of Eels

Reputation: 285401

You can only access the methods that the variable has available, and Object has none of those methods. That is why you should not be using Object in this way. Yes, the object the variable holds is a JLabel, but the compiler knows that the variable can hold an object of any type, and so to be safe, only allows Object method calls.

Possible solutions:

  • you can cast: ((JLabel) label1).setText("Foo");
  • Or better to declare label1 as a JLabel variable and declare addLabel to return a JLabel.

Upvotes: 6

Elliott Frisch
Elliott Frisch

Reputation: 201439

Because you have erased the type, you need to return a JLabel to use it as a JLabel - 

public JLabel addLabel(String text)
{
  JLabel label = new JLabel(text);
  add(label);

  return label;
}

and then

JLabel label1 = addLabel("First number");

Upvotes: 4

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