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Object Oriented Programming Articles
Page 218 of 589
What is loose coupling how do we achieve it using Java?
Coupling refers to the dependency of one object type on another, if two objects are completely independent of each other and the changes done in one doesn’t affect the other both are said to be loosely coupled.You can achieve loose coupling in Java using interfaces -Exampleinterface Animal { void child(); } class Cat implements Animal { public void child() { System.out.println("kitten"); } } class Dog implements Animal { public void child() { System.out.println("puppy"); } } public class LooseCoupling { public static void main(String args[]) { Animal obj = new Cat(); obj.child(); } }Outputkitten
Read MoreHow to access a derived class member variable by an interface object in Java?
When you try to hold the super class’s reference variable with a sub class object, using this object you can access the members of the super class only, if you try to access the members of the derived class using this reference you will get a compile time error.Exampleinterface Sample { void demoMethod1(); } public class InterfaceExample implements Sample { public void display() { System.out.println("This ia a method of the sub class"); } public void demoMethod1() { System.out.println("This is demo method-1"); } public static void main(String args[]) { ...
Read MoreWhile overriding can the subclass choose not to throw an exception in java?
If the super-class method throws certain exception, you can override it without throwing any exception.ExampleIn the following example the sampleMethod() method of the super-class throws FileNotFoundException exception and, the sampleMethod() method does not throw any exception at all. Still this program gets compiled and executed without any errors.import java.io.File; import java.io.FileNotFoundException; import java.io.IOException; import java.util.Scanner; abstract class Super { public void sampleMethod()throws FileNotFoundException { System.out.println("Method of superclass"); } } public class ExceptionsExample extends Super { public void sampleMethod() { System.out.println("Method of Subclass"); } public static void main(String args[]) { ...
Read MoreWhy should a blank final variable be explicitly initialized in all Java constructors?
A final variable which is left without initialization is known as blank final variable.Generally, we initialize instance variables in the constructor. If we miss out they will be initialized by the constructors by default values. But, the final blank variables will not be initialized with default values. So if you try to use a blank final variable without initializing in the constructor, a compile time error will be generated.Examplepublic class Student { public final String name; public void display() { System.out.println("Name of the Student: "+this.name); } public static void main(String args[]) { ...
Read MoreWhy Java wouldn't allow initialization of static final variable in a constructor?
If you declare a variable static and final you need to initialize it either at declaration or, in the static block. If you try to initialize it in the constructor, the compiler assumes that you are trying to reassign value to it and generates a compile time error −Exampleclass Data { static final int num; Data(int i) { num = i; } } public class ConstantsExample { public static void main(String args[]) { System.out.println("value of the constant: "+Data.num); } }Compile time errorConstantsExample.java:4: error: cannot assign a value to final ...
Read MoreCan a final keyword alone be used to define a constant in Java?
A constant variable is the one whose value is fixed and only one copy of it exists in the program. Once you declare a constant variable and assign value to it, you cannot change its value again throughout the program.Unlike other languages java does not support constants directly. But, you can still create a constant by declaring a variable static and final.Static − Once you declare a variable static they will be loaded into the memory at the compile time i.e. only one copy of them is available.Final − once you declare a variable final you cannot modify its value ...
Read MoreDifference between next() and hasNext() in java collections?
Java provides Iterator and ListIterator classes to retrieve the elements of the collection objects.The hasNext() methodThe hasNext() method of these interfaces returns true if the collection object has the next element else it returns false.Exampleimport java.util.ArrayList; import java.util.Iterator; public class hasNextExample{ public static void main(String[] args){ ArrayList list = new ArrayList(); //Instantiating an ArrayList object list.add("JavaFX"); list.add("Java"); Iterator it = list.iterator(); System.out.println(it.hasNext()); it.next(); System.out.println(it.hasNext()); it.next(); System.out.println(it.hasNext()); } ...
Read MoreHow to remove the redundant elements from an ArrayList object in java?
The interface set does not allow duplicate elements. The add() method of this interface accepts elements and adds to the Set object, if the addition is successful it returns true if you try to add an existing element using this method, the addition operations fails to return false.Therefore, to remove redundant elements of an ArrayList object −Get/create the required ArrayList.Create an empty set object.Try to add all the elements of the ArrayList object to set objectives.Clear the contents of the ArrayList using the clear() method.Now, using the addAll() method add the contents of the set object to the ArrayList again.Exampleimport ...
Read MoreHow to insert an object in an ArrayList at a specific position in java?
The add() method of the ArrayList class helps you to add elements to an array list. It has two variants −add(E e) − This method accepts an object/elements as a parameter and adds the given element at the end of the list.public void add(int index, E element) − This method accepts an element and an integer value representing the position at which we need to insert it and inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).Therefore ...
Read MoreDifference between peek(), poll() and remove() method of Queue interface in java?
This represents a collection that is indented to hold data before processing. It is an arrangement of the type First-In-First-Out (FIFO). The first element put in the queue is the first element taken out from it.The peek() methodThe peek() method returns the object at the top of the current queue, without removing it. If the queue is empty this method returns null.Exampleimport java.util.Iterator; import java.util.LinkedList; import java.util.Queue; public class QueueExample { public static void main(String args[]) { Queue queue = new LinkedList(); queue.add("Java"); queue.add("JavaFX"); queue.add("OpenCV"); ...
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