FirstTask

FirstTask

1. classes are the fundamental building blocks of a Java program and determine what kind of objects you get

   • a general syntax:

2. the features of objects

   • attributes are called fields - optional
   • actions are called methods - optional the object is able to perform
     • a method has a declaration part and a body
       • the declaration part consists of a return value, the method name, and a list of arguments
       • the body contains code that perform the action
     • a general syntax
       • the return type of a method can be a primitive, an object, or void void - the method returns nothing
     • a special method called main
       • the signature of the main method
       • pass arguments to main: type arguments after the class name e.g. to pass two arguments, "1" and "safeMode" when running the Test class
   • methods and fields capitalize the initial of each name, except the first word e.g. macAge - Camel naming convention

3. class names capitalize the initial of each name e.g. DataUtility - Pascal naming convention

4. UML class diagrams: the topmost part - the class name, the middle part - the list of fields, and the bottom part - the list of methods

5. an object can contain other objects if the class of the former contains variables that reference to the latter

6. every class have at least one constructor

   • a constructor
     • does not have return value
     • must have the same name as the class
     • may have zero argument (no-arg)
     • a general syntax

7. create objects

   • to create an Employee object: new Employee () ;
   • to assign an object variable: Employee employee = new Employee () ;
   • to call a method or a field by using a period: objectReference . methodName objectReference . fieldName
     • creates an Employee object and assigns values to its age and salary fields

8. a reference variable refers to an object

   • a reference variable does not have value, which is not referencing an object
     • declare a local reference variable within a method but do not assign an object to it, need to assign null to it to satisfy the compiler

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