Visibility Modifiers and Accessors in Java

Visibility Modifiers

• Public visibility allows referencing members anywhere.
• Private visibility restricts referencing members to within the class.
• Members without a visibility modifier have default visibility, allowing referencing by classes in the same package.
• Public variables violate encapsulation because they allow direct manipulation of values by clients.
• Instance variables should not be declared with public visibility.
• Public constants do not violate encapsulation, as clients cannot modify their values.
• Public methods, also known as service methods, provide object services to clients.
• Support methods are internal, not intended for client calls, thus declared with non-public visibility.

Accessors and Mutators

• Accessor methods retrieve the current value of a variable.
• Mutator methods modify the value of a variable.
• Accessor method names usually follow the pattern getX, where X is the variable name.
• Mutator method names usually follow the setX pattern.
• These methods are often called "getters" and "setters".

Mutator Restrictions

• Mutators allow controlling how clients modify an object's state.
• They can enforce limits on variable values, preventing invalid assignments.

Methods

• A method declaration specifies the code executed when the method is invoked (called).
• When invoked, control jumps to the method, executes its code, and returns to the calling location.
• Methods can return a value or not, depending on the definition.
• If the called method is in the same class, only the method name is required for invocation.
• If the method is in another class or object, the object name and method are used for invocation.

Method Header

• A method declaration starts with a method header.
• It includes the method's modifier, return type, name, and parameter list.
• The parameter list specifies the type and name of each parameter.
• Parameter names in the method declaration are known as formal parameters.

Method Body

• The method body follows the header.
• It contains the code to be executed when the method is invoked.
• Local data declared within the method body are created when the method is called and destroyed when it finishes.

The return Statement

• The return type of a method indicates the type of value it returns to the caller.
• Methods that do not return a value have a void return type.
• The return statement specifies the value to be returned.
• The return expression must match the method's return type.

Parameters

• When a method is called, the provided actual parameters in the invocation are copied to the formal parameters in the method header.
• Each parameter in the invocation is matched with its corresponding formal parameter in the method header.

Classes

• The values of an object's data define its state.
• An object's methods define its behaviors.
• Any specific program may not use all operations provided by a class.