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Java Articles
Page 349 of 450
How to declare a constructor in Java?
While declaring the constructors you should keep the following points in mind.A constructor does not have a return type.The name of the constructor is same as the name of the class. A class can have more than one constructor.Examplepublic class Sample { int num; public Sample() { num = 30; } public Sample(int value) { num = value; } }
Read MoreWhat are the different types of keywords in Java?
Following are the different types of keywords in java—Access modifiers − private, protected, public.Class, method, variable modifiers− abstract, class, extends, final, implements, interface, native, new, static, strictfp, synchronized, transient, volatile.Flow control− break, case, continue, default, do, else, for, if, instanceof, return, switch, while.Package control− import, package.Primitive types− boolean, byte, char, double, float, int, long, short.Error handling− assert, catch, finally, throw, throws, try.Enumeration− enum.Others− super, this, void.Unused− const, goto.
Read MoreWhat is the difference between keywords and reserved words in Java?
KeywordsKeywords in Java convey a special meaning to the compiler therefore, these cannot be used as identifiers. Java provides a set of 50 keywords.abstractcontinuefornewswitchassertdefaultgotopackagesynchronizedbooleandoifprivatethisbreakdoubleimplementsprotectedthrowbyteelseimportpublicthrowscaseenuminstanceofreturntransientcatchextendsintshorttrycharfinallongstrictfpvolatileconstfloatnativesuperwhileReserved wordsAmong the list of key words list mentioned above the key words goto and const are currently not in use. They are reserved words (for the future use).
Read MoreWhat environment variables do I need to set up before I start running Java programs on my machine?
Before running Java programs on your machine you need to set two environment variables namely, PATH − The path environment variable is used to specify the set of directories which contains execution programs.When you try to execute a program from command line, the operating system searches for the specified program in the current directly, if available, executes it.In case the programs are not available in the current directory, operating system verifies in the set of directories specified in the ‘PATH’ environment variable.CLASSPATH − The classpath environment variable is used to specify the location of the classes and packages.When we try ...
Read MoreWhat is a Java class library?
Java is not dependent on any specific operating system so Java applications cannot depend on the platform dependent native libraries, therefore, instead of those Java provides a set of dynamically loaded libraries that are common to modern operating systems.These libraries provide –Container classes and Regular Expressions.Interfaces for tasks that depend on the hardware of the OS such as network and file access.In case, the underlying platform does not support certain feature of Java then, these libraries surpass that specific feature if needed.
Read MoreHow many packages and classes are there in Java Standard Edition 8?
Java Standard Edition provides 14 packages namely –applet − This package provides classes and methods to create and communicate with the applets.awt− This package provides classes and methods to create user interfaces.beans− This package contains classes and methods to develop components based on java beans. io− This package contains classes and methods to read and write data standard input and output devices, streams and files.lang− This package contains the fundamental classes, methods, and, interfaces of Java language.math− This package contains classes and methods which helps you to perform arithmetic operations using the Java language.net− This package provides classes to implement ...
Read MoreWhy Java is not a pure object oriented programming language?
A fully object-oriented language needs to have all the 4 oops concepts. In addition to that, all predefined and, user-defined types must be objects and, all the operations should be performed only by calling the methods of a class.Though java follows all the four object-oriented concepts,Java has predefined primitive data types (which are not objects).You can access the members of a static class without creating an object of it.Therefore, Java is not considered as fully object-oriented Technology.
Read MoreHow can we sort a JSONObject in Java?
A JSONObject is an unordered collection of a key, value pairs, and the values can be any of these types like Boolean, JSONArray, JSONObject, Number and String. The constructor of a JSONObject can be used to convert an external form JSON text into an internal form whose values can be retrieved with the get() and opt() methods or to convert values into a JSON text using the put() and toString() methods.In the below example, we can sort the values of a JSONObject in the descending order.Exampleimport org.json.*; import java.util.*; public class JSonObjectSortingTest { public static void main(String[] ...
Read MoreHow to access the private methods of a class from outside of the class in Java?
You can access the private methods of a class using java reflection package.Step1 − Instantiate the Method class of the java.lang.reflect package by passing the method name of the method which is declared private.Step2 − Set the method accessible by passing value true to the setAccessible() method.Step3 − Finally, invoke the method using the invoke() method.Exampleimport java.lang.reflect.Method; public class DemoTest { private void sampleMethod() { System.out.println("hello"); } } public class SampleTest { public static void main(String args[]) throws Exception { Class c = Class.forName("DemoTest"); Object obj = c.newInstance(); ...
Read MoreHow many ways can get the instance of a Class class in Java?
You can create an object of the class named Class in two ways −Using new keyword as −Class obj = new Class();Using the forName() method of the class named Class.Class obj = Class.forName("DemoTest");
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