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Java Articles
Page 449 of 450
What 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 ...
Read MoreDo local variables in Java have default values?
No, local variables do not have default values. Once we create a local variable we must initialize it before using it. Since the local variables in Java are stored in stack in JVM there is a chance of getting the previous value as default value. Therefore, In Java default values for local variables are not allowed. Example public class Sample { public static void main(String args[] ){ int data; System.out.println(data); } } Error C:\Sample>javac Sample.java Sample.java:4: error: variable data might not have been initialized System.out.println(data); ^ 1 error
Read MoreWhat does abstract modifier in Java do?
An abstract keyword is used to declare methods abstract methods and abstract classes. Once a method is declared abstract we should not specify body for those. Example public abstract class Sample{ public abstract demo(){ } } Error Sample.java:2: error: invalid method declaration; return type required public abstract demo(){ ^ 1 error And once a class is declared abstract it cannot be instantiated. Example public abstract class Sample{ public abstract void demo(); public static void main(String args[]){ new Sample(); } } Error C:\Sample>javac Sample.java Sample.java:4: error: Sample is abstract; cannot be instantiated new Sample(); ^ 1 error
Read MoreHow many ways a String object can be created in java?
You can create a String by − Step 1 − Assigning a string value wrapped in " " to a String type variable. String message = "Hello Welcome to Tutorialspoint"; Step 2 − Creating an object of the String class using the new keyword by passing the string value as a parameter of its constructor. String message = new String ("Hello Welcome to Tutorialspoint"); Step 3 − Passing a character array to the String constructor. char arr[] = {'H','e','l','l','o'}; String message = new String(arr);
Read MoreHow to create a string from a Java ArrayList?
To convert the contents of an ArrayList to a String, create a StringBuffer object append the contents of the ArrayList to it, finally convert the StringBuffer object to String using the toString() method. Example import java.util.ArrayList; public class String_ArrayList { public static void main(String args[]) { ArrayList al = new ArrayList(); al.add("Hello"); al.add("are"); al.add("you"); StringBuffer sb = new StringBuffer(); for (String s : al) { sb.append(s); sb.append(" "); } String str = sb.toString(); System.out.println(str); } } Output Hello are you
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