use java please

Why does println() in the code below displays three different messages? To explain this you need to recall automatic type casting and associatively of operators. class PrintTest. {public static void main (string [] arga) {int a = 2, b = 3; System.out.println {"a + b = "+a + b); System.out.println ("a + b + " a + b "); System.out.println (a + b + "a + b ");}}