Java Tutorial

Java Tutorial Java Features C++ vs Java Java History Java Hello World Java Development Kit Java Runtime Environment Java Virtual Machine Difference between JDK, JRE, and JVM Memory Areas in Java Java Operators Java Keywords Primitive Data Types Variables

Java Loops

Java Do While Loop Java While Loop Java For Loop Java Enhanced For Loop

Java Programs

Java Basic Programs Factorial Program in Java Fibonacci Series Program in Java Prime Number Program in Java Palindrome Number Program in Java Armstrong Number Program in Java Anagram Program in Java Pattern Programs in Java Calculator Program in Java Leap Year Program in Java Addition Program in Java Number Pattern Programs in Java Star Pattern Programs in Java Package Program in Java Pyramid Program in Java Sorting Program in Java String Palindrome Program in Java Even Odd Program in Java For Loop Program in Java If Else Program in Java Switch Case Program in Java GCD Program in Java LCM Program in Java Hello Program in Java Matrix Program in Java Menu Driven Program in Java Series Program in Java Client Server Program in Java Swapping Program in Java Pig Latin Program in Java Tower of Hanoi Program in Java Recursion Program in Java Matrix Multiplication Program in Java Perfect Number Program in Java Classes and Objects in Java Example Programs String Programs in Java Array Programs in Java Constructor Program in Java Inheritance Program in Java Abstract class Program in Java Interface Program in Java Encapsulation Program in Java Polymorphism Program in Java Exception Handling Program in Java Multithreading Program in Java Thread Program in Java Collection Programs in Java ArrayList Program in Java Stack Program in Java Applet Program in Java Swing Program in Java JDBC Program in Java How to run Java program in command prompt How to run Java program in Eclipse Program to find and replace characters on string in java Program to find the duplicate characters in a string Program to check whether a given character is present in a string or not Java Program to Print Permutations of String Java program to find frequency of characters in a string Java Program to remove duplicate characters in a string

Java Sorting

Sorting Algorithms in Java Merge Sort in Java Quick Sort in Java Bubble Sort in Java Insertion Sort in Java Selection Sort in Java Heap Sort in Java Radix Sort in Java Topological Sort in Java Bucket Sort in Java Counting Sort in Java

Java OOPs Concepts

OOPs - Object Oriented Programming Objects and Classes in Java Methods in Java Java Naming Conventions Constructors in Java Java this keyword Java static keyword Inheritance in Java Aggregation in Java Java super keyword Constructor Chaining and Constructor Overloading Java Polymorphism Static and Dynamic Binding in Java Java Abstraction Abstract class in Java Interface in Java Difference between Abstract class and Interface Java final keyword Packages in Java Access Modifiers in Java Java Wrapper classes Java Numbers Java Characters Java Integer Java Boolean Java Arrays Java Command Line Arguments Java strictfp Keyword Java Math

Java Strings

Java Strings Java String Methods StringBuilder in Java StringBuffer in Java Java Regular Expressions StringBuffer vs StringBuilder String vs StringBuffer String vs StringBuilder String Manipulation in Java Java String Concatenation How to Reverse a String in Java String Array in Java How to Compare Two Strings in Java How to Concatenate Two Strings in Java Why String in Immutable in Java Java.lang.NumberFormatException for Input String String Pool in Java Java Generate Random String How to take String Input in Java Java String Interview Questions

Java Exceptions

Exception Handling in Java Java try catch Java throw Java throws Difference between throw and throws Java finally Java Custom Exception Java Exception Propagation

Garbage Collection

Automatic Resource Management in Java Java Garbage Collection Java finalize() Java gc() Difference between final, finally and finalize


Multithreading in Java Process and Thread in Java Basic Terms in Multithreading Java Thread creation Thread Scheduler in Java Java Thread class DeadLock in Java

Java IO

Java IO Java Read File Java file Reader Java Buffer Reader Java file Writer Java BufferedWriter Java InputStreamReader Scanner in Java Java StringReader Java StringReader Class Java PrintWriter Java File Java Read File Line By Line Java FileInputStream Java FileOutputStream Java Create File Java Delete File Java Open File Java Read File to String Java copy file Java Read JSON file Jar File in Java Java FileNotFoundException


Java Serialization Java transient


Java Network Programming Java Socket Programming Java URL Java URLConnection HttpURLConnection in Java Java InetAddress Java DatagramSocket and Java DatagramPacket


Java AWT


Swing in Java

Java Collections

Collections in Java Java List Interface ArrayList in Java LinkedList in Java Vector in Java Stack in Java ArrayList vs LinkedList in Java ArrayList vs Vector in Java Java Set Interface HashSet in Java LinkedHashSet in Java TreeSet in Java Java Queue Interface PriorityQueue in Java ArrayDeque in Java Java Map Interface HashMap in Java LinkedHashMap in Java TreeMap in Java Dictionary in Java Hashtable in Java Properties in Java Collections class in Java Java Comparable Java Comparator Comparable vs Comparator in Java

Java Generics

Generics in Java

Java Annotations

Annotations in Java


Java JDBC Tutorial JDBC Architecture Types of JDBC Drivers JDBC vs ODBC Java Database Connectivity with MySQL Statements in java Prepared statement in Java Resultset in java Java ResultSetMetaData DatabaseMetaData in Java Callable Statement in Java Transaction Management in java

Java Differences

Java vs JavaScript Python vs Java Kotlin vs Java Java vs C++ C# vs Java Static vs Non-static in Java C vs Java int vs Integer in Java Stack vs Heap in Java Java Array vs ArrayList

How to

How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to add double quotes in a string in Java How to convert list to String in Java How to call a method in Java How to sort an array in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to create thread in Java How to find length of String in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to find the length of an Array in Java How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to create custom exception in Java How to import packages in Java How to run applet Program in Java How to take Array Input in Java How to achieve abstraction in Java How to call static method in Java How to compare characters in Java How to initialize string array in Java How to Install Java on MAC How to run java program in ubuntu How to find characters with the maximum number of times in a string java How to Set Java_home in Linux How to Split the String in Java with Delimiter How to Split String by Comma in Java How to remove special characters from String in Java How to remove last character from String in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Parallel Arrays Sort in Java

Java 9 Features

Java 9 Tutorial Java 9 Try With Resources Java 9 Interface Private Method

Java Servlet Tutorial

Java Servlets Tutorial

Java JSP Tutorial

Java JSP Tutorial

Hibernate Tutorial

Hibernate Tutorial

Spring Tutorial

Spring Tutorial

Spring MVC Tutorial

Spring MVC Tutorial

Jenkins Tutorial

Jenkins Tutorial

Java Math Methods

Math.abs() Math.acos() Math.addExact() Math.asin() Math.atan () Math.atan2() Math.cbrt() Math.ceil() Math.copysign() Math.cos() Math.cosh() Math.decrementExact() Math.exp() Math.expm1() Math.floor() Math.floorDiv() Math.floorMod() Math.getExponent() Math.hypot() Math.IEEEremainder() Math.incrementExact() Math.log() Math.log10() Math.log1p() Math.max() Math.min() Math.multiplyExact() Math.multiplyFull() Math.negateExact() Math.nextAfter() Math.nextDown() Math.nextUp() Math.pow() Math.random() Math.rint() Math.round() Math.scalb() Math.signum() Math.sin() Math.sinh() Math.sqrt() Math.subtractExact() Math.tan() Math.tanh() Math.toDegrees() Math.toIntExact() Math.toRadians() Math.ulp()

Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

Java Convert String to int Java Convert int to String Java Convert String to long Java Convert long to String Java Convert String to float Java Convert float to String Java Convert String to double Java Convert double to String Java Convert String to Date Java Convert Date to String Java Convert String to Object Java Convert Object to String Java Convert String to char Java Convert char to String Java Convert int to long Java Convert long to int


Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java What are Array strings in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Char and String differences in Java Difference between String, StringBuffer and StringBuilder in java Replace character in string Java String Coding Interview Questions in Java What is String in Java? String isnullorempty in Java String Matches in Java Trim Method in String Java Bean class in Java Libraries in Java Arithmetic Operations on String in Java Convert Char array to string in java Check whether Java is installed or not How to calculate time difference in Java How to stop execution after a certain time in Java Jagged Array in Java Java ArraylistRemove() Time Complexity Java Swing Time Picker Zigzag Array in Java Array and String based questions in Java Array and String with Examples in Java Best Practices to use String Class in Java What is string in Java why it's immutable Java String Java String Inbuilt functions Java String Matches vs Contains Sum of digits in string in java Check the presence of Substring in a String in java Java import packages Interfaces and Classes in Strings in Java Maximum length of string in java Hidden classes in Java Class memory in Java public static void main string args meaning in java Reverse a String in Java String Concatenation in Java Difference between String and Char Array in Java Buffer reader to read string in Java

Java Garbage Collection

Java Garbage Collection

In Java, unreferenced objects are treated like garbage. The process of reclaiming the unused memory during runtime automatically is known as the Java Garbage Collection.In other words, the Java Garbage Collection is used to destroy the reference less or unused objects. In this section, we are going to discuss what is garbage collection in Java.

What is Java Garbage Collection?

  • Java garbage collection is a feature used in Java that releases the runtime unused memory by destroying the unreferenced objects.
  • To achieve the same in C, one has to use the free() function, and the delete() function is used in C++.
  • But in Java, the garbage collector runs automatically while the program is in execution.
  • The garbage collector resides inside the JVM (Java Virtual Machine).

However, in Java, the garbage collection is done automatically. Hence, Java has better memory management as compared to C and C++.

Why Java Garbage Collection is required?

In languages like C++, it is the responsibility of the programmer to create as well destruct the objects. Many times, it is observed that the programmer created the objects but forgot to destruct the objects. Because of this negligence, at the specific point of time, there will be a shortage of memory for the creation of more objects, and this may lead to abnormal termination of the program because of OutOfMemoryErrors. Hence, to get rid of such errors, Garbage Collection is introduced in Java, that works automatically and does the destruction of unreachable or reference less objects.

The heap memory has two types of objects as follows:

  1. Live object:An object that is live in heap memory and referencing to any objectis known as live object.
  2. Dead object:An object that is no longer assigned anywhere is known as dead object.

How objects are dereferenced?

We can use the following ways to make an unused object valid for garbage collection:

  1. By making a reference null

Consider the example, a class named Employee is declared having an object named emp.

 public class Employee
 Employee emp= new Employee();
 emp= null;

The second line of code makes the object emp be dereferenced.

  • Assigning an old reference to a new reference:

          Consider the example, a class named Employee is declared having two objects named emp1 and emp2.

 public class Employee
 Employee emp1 = new Employee();
 Employee emp2 = new Employee();

In the above code snippet,the last statement reassigned the object emp2 to emp1. It means thatthe abject emp1 can be removed from the memory as it does not have any new reference.

  • With the use of anonymous objects

Consider the example, a class named ‘Employee’ is declared having an object named emp.

new Employee();

There is no name to this object therefore it is valid for garbage collection.

How does the Java Garbage Collector work?

The Java garbage collector runs inside the JVM (Java Virtual Machine). Each JVM has its own version of the garbage collector. The garbage collector must satisfy the standard JVM specifications of working with the object stored in the memory heap, identifying the unreachable objects, destroying them, and compacting the memory once again.

Oracle provides a JVM named HotSpot. It has a powerful and full-fledged garbage collection option. It follows the same procedure as followed by other garbage collectors.It identifies the unreferenced objects and marks those objects for garbage collection.After that, it removes them and at last performs defragmentation on the heap memory. So that remaining objects are compacted in a contiguous memory space at the start of the memory heap.

Java Garbage Collection

The memory heap is divided into three sections:

  1. Young Generation:

The newly created objects are of the young generation. It is divided into two parts i.e. Eden and Survivor Space. In Eden, the newly generated objects are stored whilethe survivor spaces S0 and S1 have those objects that are gone through the first garbage collection cycle. The garbage collection performed in this generation is a minor garbage collection event.

  • Old Generation:

The objects that are no longer used in the program are shifted to the old generation from the young generation. These objects’ removal is called a major garbage collection event.

  • Permanent Generation:

Metadata that consists of different classes and methods is considered as a permanent generation. Removing the unused classes results in permanent garbage collection.

Advantages of Java Garbage Collection

  1. As we know programming languages like C and C++ require handling memory management manually, it becomes hectic. But Java does perform this functionality automatically with the help of JVM.  So, the programmer need not to take care of the memorymanagement.
  2. If the program contains dereferenced memory objects it may lead to memory exhaustion over a longer period of time.
  3. Garbage collection reduces certain bugs like dangling pointer bugs, memory leaks, and double-free bugs.

Disadvantages of Java Garbage Collection

  1. The garbage collector stops the execution of an entire program in order to search and collect the garbage objects. It may cause longer pauses in the case of large programs and sometimes the user may notice the same.
  2. We never know when and how long the garbage collector will run to perform its task. It might impact the performance of the software.

In this section, we have discussed about Java garbage collection and its working. In the coming section we discuss about Java gc().