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By Java Tutor, on October 26th, 2011
Let’s define a constructor for the Circle class example we just saw. This constructor enables you to specify the radius of the new Circle_class object. Also, the constructor uses a ‘this’ parameter that distinguishes the method parameter from a instance field, both having the same name.
public class Circle_class
{
public static final double PI_constant = 3.14159; // Here, PI is a constant
public double radius_var1; // Here, radius_var1 is field that holds the radius of the circle
// The constructor method used to initialize the radius field
public Circle_class(double radius_var1) { this.radius_var1 = radius_var1; }
// The instance methods used to compute values based on the radius
public double circumference_of_circle()
{ return 2 * PI_constant * radius_var1; }
public double area_of_circle() { return PI_constant * radius_var1*radius_var1; }
}
A default constructor supplied by the Java compiler is explicitly initialized using the above syntax:
Circle_class c1 = new Circle_class();
c1.radius_var1 = 0.54;
In this new constructor radius_var1, the constructor is initialized at the time of object creation. This is displayed below:
Circle_class c1 = new Circle_class(0.54);
Some important points that need to be kept in mind when naming, declaring, and writing constructors are:
- The name of the constructor is always the same as the name of the class to which it belongs.
- The constructor is always declared without any return type. It is not even followed by the keyword void.
- The body of a constructor is used to initialize the ‘this’ object.
- A constructor does not return any value, not even ‘this’.
By Java Tutor, on October 21st, 2011 The Java programming language uses constructors to create and initialize objects. Let us see a simple Circle class -
Circle_class c1 = new Circle_class();
In the above code, the parenthesis is used to call a method. In the Java programming language, every class uses a constructor. A constructor is nothing but a method created by the same name as the class, to which it belongs. And can you guess what it is used for? Yes, the constructor object is used for initializing a new object. The Java class provides a default constructor that neither takes any arguments nor does it perform any initialization for the Circle class we just created.
In the example of the code we just saw, the new operator creates a new and uninitialized instance of the Circle class. The program then calls the constructor and implicitly passes a new object to it, with the help of the ‘this’ operator that we saw earlier. At the same time, it explicitly passes the arguments between the parentheses. The constructor then uses these arguments to perform any necessary initialization.
By Java Tutor, on October 15th, 2011 In the Java programming language, unlike the C language which uses a structure to create a new complex data types, classes are used to define a new data type. For example, when a new class animal is created in Java, it also implicitly creates an animal data type.
The use and assignment of the data item depends on how it was defined. For example, an item of animal data type can be assigned to a variable of type animal. It can also be passed to as a class that accepts animal as an argument.
The object-oriented programming language such as Java does not only use a data type as a simple attribute. In this type of programming, a class is represented as a hierarchy while a subclass can be shown as a special kind or a subtype of its parent class. Not only this, reference types and class are related to each other in some ways. Also, child classes always extend to their parent class and have the same functionality as the parent.
Continuing with the example we saw above, a lion class can extend to the animal class, this new type Lion is considered in the java language as a subtype of the type animal. The objects of the Lion class can also be used in places where the objects of animal class can be used. Therefore, an object of type Lion is assignable to the variable of type Animal. This assignment of classes is known as subtype polymorphism and forms a primary feature of any object-oriented language called Java.
Going back to the Reference types, these types are always accessed by a reference, which is nothing but a handle or the name of an object. The variable of a reference type holds a reference to an object of its type or of a subtype. Similar to a pointer in C or C++ a reference is a data type which is enforced strictly and can’t be examined directly. These values are static in nature and cannot be changed except when assigned to a particular object. The reference values are automatically dereferenced in any place where they are referenced. Continue reading JAVA – Objects
By Java Tutor, on October 7th, 2011 In Java, robust classes and components are based on the object-oriented principles of encapsulation and information hiding. This approach of information hiding can be further extended by using the appropriate assessor methods.
Accessor is member functions used in java to directly manipulate the value of any field. These accessor methods are of two types:
A setter is used to modify the value of a field. On the other hand, a getter is used to obtain the field’s value. Execution of assessors involves a minimal overhead to your program’s code. Not only this, if these assessors are not used in your code, the loss of performance is often very small when compared to other factors such as databases not designed well.
However, the use of accessor benefits the code too by hiding the implementation details and by increasing the robustness of your code. A good programmer can increase the maintainability of the code by defining a getter and a setter to access a field. This leads to minimizing the effort for making any changes in the code. The getters and setters enable a programmer to encapsulate important:
- Business rules
- Transformation logic
- Validation logic applicable to the data fields of the code.
The example given below depicts the use of the setter and getter functions for the Address_of_your_Home field of the Employee class Continue reading JAVA – Getter/Accessors and Setters/Modifiers
By Java Tutor, on October 3rd, 2011 Though constructors and methods look similar to each other, they are different both in construct and syntax.
Constructors are used to create instances of a class. Constructors are created in a manner similar to objects, such as:
mari_gold m_var1= new mari_gold();
Some of the key properties that differentiate the constructor and the methods are:
- Modifiers: Like methods, constructors can also use any of the following three access modifies, such as Public, Private, and non, which is also known as package or friendly. The following types of constructors do not exist: abstract, abstract, static, final, native, or synchronized.
- Return types: Constructors do not have any kind of return types, unlike methods which can have any valid return type or at least a default value as void.
- Signature: The naming convention of constructors and methods also vary greatly. Constructors get the same name as the class name. On the other hand, methods use names that are not same as class name. If the programmers use the normal Java language conventions, constructors would always start with upper case letters, unlike methods which start with a lower case letter. Not only this, you will also notice that the names of the constructors are nouns, whereas the method names are adjectives as they indicate action.
- The use of “This” keyword: Both constructors and methods use the keyword “this” in a different manner. The keyword ‘this’ in a method refers to an instance of the class that is using the method. Also, the static methods do not belong to any instance of the class, and therefore the keyword “this” does not refer to anything in such methods. These methods belong to an entire class and not to any particular instance of the class.
Conversely, in the case of constructors, to refer to another constructor in the same class the “this” keyword is used, but having a different list of the parameters associated with it. Continue reading JAVA – Constructors
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