256 key size in AES

[Sumayah Abdul]

Hello everyone,
I'm encrypting using Symmetric keys and using the following code

 
 KeyGenerator kGen = KeyGenerator.getInstance("AES");
 kGen.init(128);
 Key key = kGen.generateKey();
 Cipher cipher = Cipher.getInstance("AES");
 String input = RandomString(5);
byte[] inputBytes = input.getBytes();

 //Encrypt
cipher.init(Cipher.ENCRYPT_MODE, key);
 byte[] cipherText = cipher.doFinal(inputBytes);
 //decrypt
       cipher.init(Cipher.DECRYPT_MODE, key);    
        byte[] plainTextBytes =  cipher.doFinal(cipherText);
   

which is working fine. but when i change the key size to 256 in

   kGen.init(256); 

I get an error at the (cipher.init(Cipher.ENCRYPT_MODE, key);) that the keysize is illegal. how can i use 256 keysize for AES?

Thank you

[Sumayah Abdul]

I found an answer
here