Question: In Java, you can create a String object as below : String str = "abc"; & String str = new String("abc");  Why cant a button object be created as : Button bt = "abc"? Why is it compulsory to create a button object as: Button bt = new Button("abc"); Why this is not compulsory in String's case?

Answer: Button bt1= "abc"; It is because "abc" is a literal string (something slightly different than a String object, by-the-way) and bt1 is a Button object. That simple. The only object in Java that can be assigned a literal String is java.lang.String. Important to not that you are NOT calling a java.lang.String constuctor when you type String s = "abc";
For example String x = "abc"; String y = "abc"; refer to the same object. While String x1 = new String("abc");
String x2 = new String("abc"); refer to two different objects.