Found 346 Articles for Java Programming

A Singleton pattern states that a class can have a single instance and multiple instances are not permitted to be created. For this purpose, we make the constructor of the class a private and return a instance via a static method. But using cloning, we can still create multiple instance of a class. See the example below −Example - Breaking Singletonpublic class Tester{    public static void main(String[] args)    throws CloneNotSupportedException {       A a = A.getInstance();       A b = (A)a.clone();       System.out.println(a.hashCode());       System.out.println(b.hashCode());    } } ... Read More

If a object is no more referenced by a live reference then it becomes eligible for garbage collection. See the example below −Examplepublic class Tester{    public static void main(String[] args) {       test();    }    public static void test(){       A a = new A();    } } class A {}When test() method complete execution, the a object is no more referenced and is eligible for garbage collection. Java garbage collector will deallocate the object when it runs.To prevent garbage collection, we can create a static reference to an object and then ... Read More

In order to find occurence of each character in a string we can use Map utility of Java.In Map a key could not be duplicate so make each character of string as key of Map and provide initial value corresponding to each key as 1 if this character does not inserted in map before.Now when a character repeats during insertion as key in Map increase its value by one.Continue this for each character untill all characters of string get inserted.Examplepublic class occurenceOfCharacter {    public static void main(String[] args) {       String str = "SSDRRRTTYYTYTR";       ... Read More

This articles covers how to encode and decode JSON objects using Java programming language. Let's start with preparing the environment to start our programming with Java for JSON.EnvironmentBefore you start with encoding and decoding JSON using Java, you need to install any of the JSON modules available. For this tutorial we have downloaded and installed JSON.simple and have added the location of json-simple-1.1.1.jar file to the environment variable CLASSPATH.Mapping between JSON and Java entitiesJSON.simple maps entities from the left side to the right side while decoding or parsing, and maps entities from the right to the left while encoding.JSONJavastringjava.lang.Stringnumberjava.lang.Numbertrue|falsejava.lang.Booleannullnullarrayjava.util.Listobjectjava.util.MapOn decoding, ... Read More

java.lang.System.currentTimeMillis() method can be used to compute the time taken by a function in java. Trick is simple. Get the before time and after time using currentTimeMillis() where before time is the time when method is invoked and after time is when method has executed. See the example below −Example Live Demopublic class Tester{    public static void main(String[] args) {       long startTime = System.currentTimeMillis();       longRunningMethod();       long endTime = System.currentTimeMillis();       System.out.println("Time taken: " + (endTime -startTime) + " ms");    }    private static void longRunningMethod() {       try {          Thread.sleep(1000);       } catch (InterruptedException e) {          e.printStackTrace();       }    } }OutputTime taken: 1000 ms

Arrays can be compared using following ways in JavaUsing Arrays.equals(array1, array2) methods − This method iterates over each value of an array and compare using equals method.Using Arrays.deepEquals(array1, array2) methods − This method iterates over each value of an array and deep compare using any overridden equals method.Using == on array will not give the desired result and it will compare them as objects. See the example below for each of the comparison way.Example Live Demoimport java.util.Arrays; public class Tester{    public static void main(String[] args) {       int[] array1 = {1, 2, 3};       int[] ... Read More

Java Garbage collector tracks the live object and objects which are no more need are marked for garbage collection. It relieves developers to think of memory allocation/deallocation issues. JVM uses the heap, for dynamic allocation. In most of the cases, the operating systems allocate the heap in advance which is then to be managed by the JVM while the program is running. It helps in following ways:  Faster object creation as Operating system level synchronization is no more needed for each object. Object Allocation takes some memory and increases the offset. When an object is not required, garbage collector ... Read More

Following are the key components and their responsibility in JVM. Classloader − Loads the class file into the JVM. Class Area − Storage areas for a class elements structure like fields, method data, code of method etc. Heap − Runtime storage allocation for objects. Stack − Storage for local variables and partial results. A stack contains frames and allocates one for each thread. Once a thread gets completed, this frame also gets destroyed. It also plays roles in method invocation and returns. PC Registers − Program Counter Registers contains the address of an instruction that JVM is currently ... Read More

Call by Value means calling a method with a parameter as value. Through this, the argument value is passed to the parameter.While Call by Reference means calling a method with a parameter as a reference. Through this, the argument reference is passed to the parameter.In call by value, the modification done to the parameter passed does not reflect in the caller's scope while in the call by reference, the modification done to the parameter passed are persistent and changes are reflected in the caller's scope. But Java uses only call by value. It creates a copy of references and pass ... Read More

When you compile Java programs using javac compiler it generates bytecode. We need to execute this bytecode using JVM (Java Virtual machine) Then, JVM translates the Java bytecode to machine understandable code. You can download JVM's (comes along with JDK or JRE) suitable to your operating system and, once you write a Java program you can run it on any system using JVM.