Your initializeKey() method creates a random key each time it is called. Your encryptValue() method calls initializeKey() and creates a random key to encrypt with. Your decryptValue() method calls initializeKey() and creates another random, most probably different key from that used in the encryption key, to decrypt with. AES must use the same key for encryption and decryption.
The key should be generated once and saved. You can use a password protected
Java Keystore for this.
P.S. You do realise that ECB block mode is considered insecure since it allows forgery though splicing.
You should change to use one of the feedback modes such as CBC; this will eliminate this particular insecurity.