Object Oriented ProgrammingLecture (4.1)

SupervisorEbtsam AbdelHakam

ebtsamabd@gmail.comDepartment of Computer

ScienceNajran University

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Outline» Method overloading» Method overloading benefits» Constructor overloading» Using objects as parameter

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Method Overloading

● Method overloading is to define two or more methods within the same class that share the same name, as long as their parameter declarations are different.

● Method overloading is one of the ways that Java supports polymorphism.

● When an overloaded method is invoked, Java uses the type and/or number of arguments as its guide to determine which version of the overloaded method to actually call.

● Thus, overloaded methods must differ in the type and/or number of their parameters.

● While overloaded methods may have different return types, the return type alone is insufficient to distinguish two versions of a method.

● When Java encounters a call to an overloaded method, it simply executes the version of the method whose parameters match the arguments used in the call.

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Overloading method example24

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Overloading example analysis● The value of overloading is that it allows related

methods to be accessed by use of a common name.● As you can see, test( ) is overloaded four times. ● The first version takes no parameters, the second

takes one integer parameter, the third takes two integer parameters, and the fourth takes one double parameter.

● The fact that the fourth version of test( ) also returns a value is of no consequence relative to overloading, since return types do not play a role in overload resolution.

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Method overloading benefits

● Method overloading is an applying to polymorphism concept.

● The value of overloading is that it allows related methods to be accessed by use of a common name.

● It is left to the compiler to choose the right specific version for a particular circumstance.

● For example, you can use the name sqrt to create methods that return the square of an integer and the square root of a floating-point value.

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Analysis

● As you can see, the Box( , , ) constructor requires three parameters.

● This means that all declarations of Box objects must pass three arguments to the Box() constructor.

● For example, the following statement is currently invalid:

● Box ob = new Box();● Since Box() requires three arguments, it’s an error to

call it without them.● Note that default constructor Box() can't be called,

when you define your constructor.

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Constructor Overloading

● In addition to overloading normal methods, you can also overload constructor methods.

● Constructor overloading: Same constructor declared with different parameters in the same class.

● Compiler differentiates which constructor is to be called depending upon the number of parameters and their sequence of data types.

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Using Objects as Parameters

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Using object as constructor parameter

● One of the most common uses of object parameters involves constructors.

● Frequently, you will want to construct a new object so that it is initially the same as some existing object.

● To do this, you must define a constructor that takes an object of its class as a parameter.

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this() with Constructors

» Suppose by accessing one constructor, the programmer may require the functionality of other constructors also but by creating one object only.

» "this()" is used to access one constructor from another "within the same class". Depending on the parameters supplied, the suitable constructor is accessed.

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Rules of using this()

» If included, this() statement must be the first one in the constructor. You cannot write anything before this() in the constructor.

» With the above rule, there cannot be two this() statements in the same constructor (because both cannot be the first).

» this() must be used with constructors only, that too to call the same class constructor (but not super class constructor).

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