These types of problems of different ways of initializing an object can be solved by constructor overloading. From the above implementation of Box class these options are not available to us. Suppose we simply wanted a box object without initial dimension, or want to to initialize a cube by specifying only one value that would be used for all three dimensions. Since Box() requires three arguments, it’s an error to call it without them. For example, the following statement is currently invalid: This means that all declarations of Box objects must pass three arguments to the Box() constructor. An example class to understand need ofĪs we can see that the Box() constructor requires three parameters. Consider the following implementation of a class Box with only one constructor taking three arguments. Let us take an example to understand need of constructor overloading. If we do not want to specify anything about a thread then we can simply use default constructor of Thread class, however if we need to specify thread name, then we may call the parameterized constructor of Thread class with a String args like this: For example, Thread class has 8 types of constructors. This can be done using constructor overloading. Java method signature components are as follows:ĭataBaseReader class diagram lists two constructors.Sometimes there is a need of initializing an object in different ways. Method signature does not include the return type. Method signature consists method name and a parameter list. Method overloading means that the same method name is used over and over again,īut method signature is different every time. Planet saturn = new Planet ( satellites, distance, mass ) Our objects can be constructed in many different ways.įor example, constructor of the class Planet could take a set of initial parameters, such as On the other hand, many programmers prefer to code it for documentation purposes anyway. Often there is no reason to code default constructor because it would have the same functionality as the compiler-provided constructor. The classes get a default constructor provided by Java. Public Planet( int distance, int satellites, double mass ) When data attributes are added to object implementation, each constructor needs to be updated. That is, initialization of the data member attributes. One of the most common and rudimentary activities inside a constructor is initialization of the object memory. In Java keyword new creates a new instance of an object:Įmpty parentheses in the above code specify that constructor of the Planet class does not take any arguments.Ĭonstructor with no parameters is called default constructor.Īlternatively, constructors could have a list of parameters required to properly initialize the object. Programmer is responsible for initialization of the object instance. Memory is allocated before constructor is invoked. Planet saturn = new Planet() // Java code If name is the same as the class name, then this is a constructor.Ī significant difference between constructors and other operations is that constructors don't have a return value.Īny time when the object is created. Week 5, Chapter 3, Advanced Concepts: Constructors, Overloading, ExceptionsĬonstructors are special operations that help to create and initialize objects.Ĭompilers recognize that an operation is a constructor by looking at the name: Week 5, Chapter 3, Advanced Concepts: Constructors, Overloading, Exceptionsġ.Chapter 3, Advanced Concepts: Constructors, Overloading, Exceptions
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