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Object Oriented Programming Articles
Page 587 of 589
Can interfaces have constructors in Java?
No, interfaces can’t have constructors for the following reasons − All the members of an interface are abstract, and since a constructor cannot be abstract. Still, if you try to write a constructor within an interface it will generate a compile time error. Example public interface InterfaceTest { InterfaceTest(){ } public abstract void display(); public abstract void show(); } Error C:\Sample>javac InterfaceTest.java InterfaceTest.java:2: error: expected public InterfaceTest(){ ^ 1 error
Read MoreHow many public classes of the same name it can have in Java?
A Java file contains only one public class with a particular name. If you create another class with same name it will be a duplicate class. Still if you try to create such class then the compiler will generate a compile time error. Example public class Example { } public class Example{ public void sample(){ System.out.println("sample method of the Example class"); } public void demo(){ System.out.println("demo method of the Example class"); } ...
Read MoreHow to print new line in Java?
The java.io.PrintStream.println() method prints an array of characters and then terminate the line. This method behaves as though it invokes print(char[]) and then println(). Using this method you can print the data on the console. import java.io.*; public class PrintStreamDemo { public static void main(String[] args) { char[] c = {'a', 'b', 'c'}; // create print stream object PrintStream ps = new PrintStream(System.out); // print an array and change line ps.println(c); ps.print("New Line"); // flush the stream ps.flush(); } } Output abc New Line
Read MoreWhat is the difference between a Java method and a native method?
A native method is the one whose method implementation is done in other languages like c++ and Java. These programs are linked to Java using JNI or JNA interfaces. The difference between normal method and native method is That the native method declaration contains native keyword and, the implementation of the method will be other programming language. Example Tester.java public class Tester { public native int getValue(int i); public static void main(String[] args) { System.loadLibrary("Tester"); System.out.println(new Tester().getValue(2)); ...
Read MoreWhat is the purpose of System class in Java?
System class belongs to the package java.lang. It cannot be instantiated. A System class provides − standard output. error output streams. standard input and access to externally defined properties and environment variables. A utility method for quickly copying a portion of an array. a means of loading files and libraries. Following are the fields for java.lang.System class − static PrintStream err − This is the "standard" error output stream. static InputStream in − This is the "standard" input stream. static PrintStream out − This is the "standard" output stream.
Read MoreHow to count unique elements in the array using java?
The interface Set does not allow duplicate elements, therefore, create a set object and try to add each element to it using the add() method in case of repetition of elements this method returns false − If you try to add all the elements of the array to a Set, it accepts only unique elements − Example import java.util.Arrays; import java.util.HashSet; import java.util.Scanner; import java.util.Set; public class CountingUniqueElements { public static void main(String args[]) { Scanner sc = new Scanner(System.in); System.out.println("Enter the size ...
Read MoreHow to check a String for palindrome using arrays in java?
To verify whether the given string is a palindrome (using arrays) Convert the given string into a character array using the toCharArray() method. Make a copy of this array. Reverse the array. Compare the original array and the reversed array. in case of match given string is a palindrome. Example import java.util.Arrays; import java.util.Scanner; public class Palindrome { public static void main(String args[]) { System.out.println("Enter a string "); Scanner sc = new Scanner(System.in); String s ...
Read MoreIs final method inherited in Java?
No, we cannot override a final method in Java. The final modifier for finalizing the implementations of classes, methods, and variables. We can declare a method as final, once you declare a method final it cannot be overridden. So, you cannot modify a final method from a sub class. The main intention of making a method final would be that the content of the method should not be changed by any outsider. Example class Demo{ public final void demoMethod(){ System.out.println("Hello"); } } public class Sample extends Demo{ ...
Read MoreWhat are reference data types in Java?
Reference datatypes in java are those which contains reference/address of dynamically created objects. These are not predefined like primitive data types. Following are the reference types in Java. class types − This reference type points to an object of a class. array types − This reference type points to an array. interface types − This reference type points to an object of a class which implements an interface. Once we create a variable of these types (i.e. when we create an array or object, class or interface). These variables only store the address of these values. Default ...
Read MoreWhat is the difference between Java references and pointers in other languages?
Reference datatypes in java are those which contains reference/address of dynamically created objects. These are not predefined like primitive data types. Following are the reference types in Java. class types − This reference type points to an object of a class. array types − This reference type points to an array. interface types − This reference type points to an object of a class which implements an interface. Once we create a variable of these types (i.e. when we create an array or object, class or interface). These variables only store the address of these values. Default ...
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