The IdentityHashMap is one of the lesser known Map implementations from JDK. Unlike general purposes Map implementations like HashMap and LinkedHashMap, it is very special and its internal working is quite different than HashMap. The main difference between IdentityHashMap and HashMap in Java is that the former uses the equality operator (==) instead of the equals() method to compare keys. This means you need the same key object to retrieve the value from IdentityHashMap, you cannot retrieve values by using another key that is logically equal to the previous key.
How to use lsof command in Linux? Example Tutorial
Hello guys, If you want to learn how to use lsof command in Linux then you have come to the right place. In the last few article, I talk about find, grep, mailx, crontable and du command in Linux and in this article I am going to talk about another useful Linux command, the lsof command. The lsof command lists open files and that's why its named lsof. This command is very important for server side developer and IT support people who need to check which file is held by which process and find the deleted files which are hogging memory etc. It act as a useful debugging and troubleshooting tool in Linux.
How to Synchronize HashMap in Java? Collections.synchronizedMap() Example Tutorial
Hello guys, if you have used HashMap class in Java before than you will know that HashMap is not synchronized, which means you cannot use it on multi-threaded Java programs without external synchronization. In other words, if you share an instance of HashMap between multiple threads, where each of them is either adding, removing or updating entries then it's possible that HashMap may lose its structure and not behave as expected. In simple words, exposing HashMap to multiple threads can corrupt the Map and you may not able to retrieve the data you want. If you have read my earlier article about HashMap, you know that during re-sizing its possible that HashMap exposed to multiple threads, may end up in an infinite loop.
Difference between WeakHashMap , IdentityHashMap, and EnumMap in Java?
Hello guys, if you are wondering what is the difference between WeakHashMap, IdentityHashMap, and EnumMap in Java then you are at the right place. In last article, we have seen difference between HashMap, TreeMap, and LinkedHashMap in Java and in this article we will difference between WeakHashMap, EnumMap, and IdnetityHashMap in Java. Apart from popular implementation like HashMap and LinkedHashMap, java.util.Map also has some specialized implementation classes e.g. IdentifyHashMap which uses == instead of equals() method for comparing keys, WeakHashMap which uses WeakReference to wrap the key object and a key/value mapping is removed when the key is no longer referenced from elsewhere, and EnumMap where keys are Enum constants.
Java HashMap keySet() , entrySet and values() Example - Tutorial
The java.util.Map interface provides three methods keySet(), entrySet() and values() to retrieve all keys, entries (a key-value pair), and values. Since these methods directly come from the Map interface, you can use them with any of the Map implementation classes e.g. HashMap, TreeMap, LinkedHashMap, Hashtable, ConcurrentHashMap, and even with specialized Map implementations like EnumMap, WeakHashMap, and IdentityHashMap. In order to become a good Java developer, it's important to understand and remember key classes of Java API like Java's Collection framework.
What is static and instance Method in Java? Example Tutorial
Hello guys, if you have trouble understanding what is static method in Java and how to use it then you are at the right place. In this article, I will share everything I have learned bout static method in my 20 years of Java experience. Static methods are one of the important programming concepts in any programming language but unfortunately, it is also the most misunderstood and misused one. Talking about Java, almost all programmers know that. static methods belong to the class and non-static methods belong to the objects of the class, but hardly all of them understand what it means. That's why this is one of the popular weed-out questions on programming interviews.
How to use Lambda Expression and method reference in Java? Example Tutorial
Hello guys, if you are wondering what is lambda expression and method reference in Java then you are at the right place. Earlier, I have shared 10 Stream API examples and in this article, I will share everything I know about Lambda expression with you. The Lambda expression is one of the most important features of Java 8 which has opened a whole new dimension of programming paradigm in Java. It is the feature which made the Functional Programming possible in Java because now you can pass the code to a function to execute as opposed to an object. You might be a bit surprised but if you look from a developer's point of view, it is nothing but a way to pass your code to a method in Java.
Composite Design Pattern Example in Java and Object Oriented Programming
Hello guys, if you are wondering how to use Composite design pattern in Java then you are at the right place. Composite design pattern is another object oriented design pattern introduced by Gang of Four in there timeless classic book Design pattern : Elements of Reusable software. Composite pattern as name suggest is used to compose similar things together, like similar objects. It implements an interface and also contains other objects which implements the same interface, also known as containee. One of the best example of Composite pattern from Java standard library is Swing's container classes e.g. Panel, which not only are Components by themselves, but also contains other components like JButton, Label, JTable etc.
6 Advanced Comparator and Comparable Examples in Java 8
The JDK 8 release has completely changed the way you compare objects and sort them in Java. The new features of the Java 8 language e.g. lambda expression and method reference have made it easier to implement both Comparator and Comparable interface, as you don't need an Anonymous class for inline implementation. Now, you can create Comparators in just one line by using lambdas and method reference as we'll see in this article. Other features like providing default and static methods on interfaces have also made a huge difference when it comes to Comparator. They helped Java API designers to redesign and evolve existing interfaces, which wasn't possible earlier without breaking existing clients of those interfaces.
How to convert String to long in Java? Example
You can parse a String literal containing valid long value into a long primitive type using parseLong() and valueOf() method of java.lang.Long class of JDK. Though there is a couple of difference between valueOf() and parseLong() method e.g. valueOf() method return a Long object while parseLong() method return a Long object, but given we have autoboxing in Java, both method can use for parsing String to create long values. In the last article, you have learned how to convert a Long value to a String in Java, and in this tutorial, you will learn the opposite, i.e. how to parse a String to a long value in Java.
How to convert String to Double in Java and double to String with Example
There are three ways to convert a String to double value in Java, Double.parseDouble() method, Double.valueOf() method and by using new Double() constructor and then storing the resulting object into a primitive double field, autoboxing in Java will convert a Double object to the double primitive in no time. Out of all these methods, the core method is parseDouble() which is specially designed to parse a String containing floating-point value into the Double object. Rest of the methods like valueOf() and constructor uses parseDouble() internally. This method will throw NullPointerException if the string you are passing is null and NumberFormatException if String is not containing a valid double value e.g. containing alphabetic characters.
How to Read User Input and Password in Java from command line? Console Example
Hello guys, if you are wondering how to take user input from command prompt in Java like username and password then don't worry. Java provides several utilities like Scanner and BufferedReader to read input from command prompt in Java. Java 6 added a new utility class for reading input data from character based devices including command line. java.io.Console can be used to read input from command line, but unfortunately, it doesn't work on most of the IDE like Eclipse and Netbeans. As per Javadoc call to System.Console() will return attached console to JVM if it has been started interactive command prompt or it will return null if JVM has been started using a background process or scheduler job.
How to replace characters and substring in Java? String.replace(), replaceAll() and replaceFirst() Example
One of the common programming tasks is to replace characters or substring from a String object in Java. For example, you have a String "internet" and you want to replace the letter "i" with the letter "b", how do you that? Well, the String class in Java provides several methods to replace characters, CharSequence, and substring from a String in Java. You can call replace method on the String, where you want to replace characters and it will return a result where characters are replaced. What is the most important point to remember is that the result object would be a new String object?
5 Difference between Hashtable vs HashMap in Java? Answer
Hashtable vs HashMap in Java
Hashtable and HashMap are two hash-based collections in Java and are used to store objects as key-value pairs. Despite being hash-based and similar in functionality there is a significant difference between Hashtable and HashMap and without understanding those differences if you use Hashtable in place of HashMap then you may run into series of subtle programs which is hard to find and debug. Unlike the Difference between ArrayList and HashMap, Differences between Hashtable and HashMap are more subtle because both are similar kinds of collections. Before seeing the difference between HashMap and Hashtable let's see some common things between HashMap and Hashtable in Java.
Hashtable and HashMap are two hash-based collections in Java and are used to store objects as key-value pairs. Despite being hash-based and similar in functionality there is a significant difference between Hashtable and HashMap and without understanding those differences if you use Hashtable in place of HashMap then you may run into series of subtle programs which is hard to find and debug. Unlike the Difference between ArrayList and HashMap, Differences between Hashtable and HashMap are more subtle because both are similar kinds of collections. Before seeing the difference between HashMap and Hashtable let's see some common things between HashMap and Hashtable in Java.
How to write a Parameterized Method in Java using Generics? Example
Hello guys, if you are wondering how to write a parameterized method in Java using Generics then you are at right place. Earlier, I have shared Complete Java Generics tutorial as well as popular Generics Interview Questions and in this article, I will teach you how to write a parameterized method using Generics in Java step by step. A method is called a generic method if you can pass any type of parameter to it and it will function the same like it allows the same logic to be applied to different types. It's known as a type-safe method as well.
10 Examples of nslookup command in Linux and Windows
Hello guys, if you are wondering what is nslookup command and how to use in
Linux and Windows then you are at right place. In the past, I have shared
examples of
crontab,
find,
grep,
netstat, and
curl command
and In this article, I will share 10 different examples of nslookup command,
each using its different powerful command line option to give you the tool you
need to deal with networking related queries. I often use nslookup command
to convert a given IP address to hostname or a given
hostname to IP address. For example, when I see an IP address in our log file and want to find which
host that request is coming from, I use nslookup.
Difference between Polymorphism vs Inheritance in Java and Object Oriented Programming - Example
Programmers often confused among different object-oriented concepts e.g. between Composition and Inheritance, between abstraction and encapsulation, and sometimes between Polymorphism and Inheritance. In this article, we will explore the third one, Polymorphism vs Inheritance. Like in the real world, Inheritance is used to define the relationship between two classes. It's similar to the Father-Son relationship. In object-oriented programming, we have a Parent class (also known as the superclass) and a Child class (also known as the subclass). Similar to the real world, a Child inherits Parents' qualities, like its attributes, methods, and code.
How to convert ArrayList to Comma Separated or Delimited String in Java - Spring Example
Some time we need to convert ArrayList to String in Java
programming language in order to pass that String to stored procedure, any method
or any other program. Unfortunately Java
collection framework doesn't provide any direct utility method to convert ArrayList
to String
in Java. But Spring framework which is famous for dependency Injection and its
IOC container also provides API with common utilities like method to convert
Collection to String in Java. You can convert ArrayList to String using
Spring Framework's StringUtils class. StringUtils class
provide three methods to convert any collection e.g. ArrayList to String in Java,
as shown below:
10 Examples of head and tail command in Linux
Hello guys, if you are wondering how to use head and tail command in Linux then you have come to the right place. Both head and command are great tool to view content from files in Linux. As the name suggest, "head" is used to view the top portion of the file and "tail" is used to see the file content from bottom. For example when you say "head data.json" then it will display first 10 lines of the file and when you say "tail data.json" then it will display last 10 lines of the file. As a Java developer, I find myself using tail more often than head while checking logs. As you can use tail to see the last few lines of the log file and you can also use tail -f application.log to see the logs rolling in real time. I often use this command to track request and see what application is doing at a particular time.
Difference between JDK and JRE in Java Platform
Java Platform offers JRE and JDK to run Java programs. JRE stands for Java runtime environment and JDK stands for Java development kit. JRE is meant for normal users, who wants to run Java program in their computer. JRE is normally used to run Java programs downloaded over internet e.g. Java Applets and Java Desktop application built using AWT and Swing. The main difference between JRE and JDK, comes from the fact that they are different tools. JDK is created for Java programmers and contains tools required for Java programming, like javac for compiling Java source files to .class files. Without JDK, you can not create Java applications and programs.
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