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Chapter 1 - Java Program Design and Development
Monday, May 9, 2022
8:36 PM
When talking about designing an object - really just talking about designing the objects c
Class: defines the collection of objects that belong to it, the class can be considered the
To figure out what should be split into different objects look for nouns
Choosing behaviour of an object is a matter of looking for verbs
Class Name: Riddle
Role: to store and retrieve a question and answer
question - a variable to store a riddle's question (private);
answer: a variable to store a riddle's answer (private)
Riddle(): a method to set a riddle's question and answer
getQuestion(): a method to return a riddle's question
getAnswer(): a method to return a riddle's answer
Public vs Private:
- Mostly attributes (variables) are private (-)
- Operations (methods) are public (+)
Class Names:
- Begin with capital letter and use capitals for all new words Ex HelloWorld
Variable and Method Names:
- Begin with lowercase letter but also use capitals for new words Ex getQuestion
A variable’s type is either one of the primitive types we mentioned, such as int, double, or boolean, or f
name of the object’s class, such as String or HelloWorld.
- Declaring a variable will tell the program to set aside enough memory for whatever type of variab
Declaration Variable:
Type VariableName ;
HelloWorld helloWorld;
Assignment Variable:
VariableName = Value ;
Declaration Variable:
Type VariableName ;
HelloWorld helloWorld;
Assignment Variable:
VariableName = Value ;
Expressions and Operators:
+, -, < > are operators; these operators have a type that depends on the type being
manipulated; int + int will produce int
int > int will produce boolean
Be careful not to confuse = and ==. The symbol = is the assignment operator. It
assigns the value on its right-hand side to the variable on its left-hand side. The symbol == is
the equality operator. It evaluates whether the expressions on its left- and right-hand sides
have the same value and returns either true or false.
Declaring Instance Variable:
private String greeting = ”Hello , World!”;
In general, an instance variable declaration has the following syntax, some parts of which are
Modifiersopt Type VariableName InitializerExpressionopt
Defining an Instance Method:
In general, a method header takes the following form, including some parts which are
Modifiersopt ReturnType MethodName ( ParameterListopt )
Java.lang package - common package that does not need to be referred to before using one
of it's classes.
String and Object are in the java.lang class but you can just do String xxx or Object xxx you do
not have to do java.lang.String
Import package.* } allows every package be used by their abbreviated names.
Primitive Types vs Reference Types:
Reference types - holds the ADDRESS for the variable in memory
Primitive types - holds the value of the variable in memory