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Java Articles
Page 448 of 450
Can a class in Java be both final and abstract?
An abstract cannot be instantiated. Therefore to use an abstract class you need to create another class and extend the abstract class and use it. If a class is final you can’t extend it further. So, you cannot declare a class both final and abstract. Example Still if you try to do so you will get a compile time error saying “illegal combination of modifiers:” final abstract class Demo{ public final void display(){ System.out.println("Hello welcome to tutorialspoint"); } } Output C:\Sample>javac Demo.java Demo.java:1: error: illegal ...
Read MoreCan constructors be marked final, abstract or static in Java?
Except public, protected and, private constructor does not allow any other modifier. When you use a final keyword with a method or constructor it cannot be overridden. But, a constructor in Java cannot be overridden therefore, there is no need of using the final keyword with the constructor. Since you cannot override a constructor you cannot provide body to it if it is made abstract. Therefore, you cannot use abstract keyword with the constructor. If you want to invoke a member of a class before instantiating the class you need to use static before it. But, contractors are called ...
Read MoreCan a constructor be overridden in java?
If super class and sub class have same methods including name, return type and parameters, and if you try to call it using the object of the sub class Then the method in the sub class is invoked. Constructor looks like method but it is not. It does not have a return type and its name is same as the class name. But, a constructor cannot be overridden. If you try to write a super class’s constructor in the sub class compiler treats it as a method and expects a return type and generates a compile time error. Example ...
Read MoreCan 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 ...
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