• The lines:

Label prompt; // prompt user to input

TextField input; // input values here

int number; // store input value

int sum; // store sum of integers

are declarations.

• The Java language requires us to declare all data that we will use in our program before we use it.
• We declare that:
  • We want a Label object in our Addition applet named prompt.
  • A Label is an object that contains a character string to be displayed on the screen.
  • We want a TextField object in our applet named input.
  • Text fields are used to either get information from the keyboard or display information on the screen.
  • We want to use 2 variables (of type int)in our Addition applet, and we will name them number and sum.
• A variable is like an object that is built into the Java system and has no formal methods. It's just a data item.
• Objects can be defined in terms of other objects.
• But, what are these other objects defined in terms of?
• The most basic objects are defined in terms of variables, Java's built-in data types.
• Each declaration is a statement in Java, terminated with a semicolon.
• The name we give to a particular object or variable, aka an identifier comprises a sequence of letters, digits, underscores (_), and dollar signs ($).
• It cannot begin witha digit.
• Java is case-sensitive, so, e.g., the name Textfield is not the same name as TextField.
• Use names that describe what the object or variable represents;
• It makes your program easier to understand, and clarity is of great value.