How to add elements to a hashmap in Java?
Use the put() method to add elements to a HashMap in Java. In this post, we’ll learn more than just how to add elements to a HashMap in Java. How …
Learn MoreJava
How to convert a String to int in Java?
Query: My String contains only numbers, and I want to return the number it represents. For example, given the string “1234” the result should be the number 1234. In this post, I’ll convert …
Learn MoreWhat is serialVersionUID in Java?
Query explained: Eclipse issues warnings when a serialVersionUID is missing. The serializable class Foo does not declare a static final serialVersionUID field of type long What is serialVersionUID and why is it important? Please …
Learn MoreWhat is dependency injection?
Dependency injection means giving an object its instance variables. Really. That’s it. The best definition I’ve found so far is one by James Shore: “Dependency Injection” is a 25-dollar term for …
Learn MoreWhat is the difference between ArrayList and LinkedList in Java?
Query: I’ve always been one to simply use: I use the interface as the type name for portability, so that when I ask questions such as these I can rework my …
Learn MoreHow to create a memory leak in Java?
Sample query: I just had an interview where I was asked to create a memory leak with Java. Needless to say, I felt pretty dumb having no clue on how to even …
Learn MoreHow to iterate over a Map in Java?
Query explained: If I have an object implementing the Map interface in Java and I wish to iterate over every pair contained within it, what is the most efficient way of going …
Learn MoreWhy is char[] preferred over String for passwords in Java?
In Swing, the password field has a getPassword() (returns char[]) method instead of the usual getText() (returns String) method. Similarly, I have come across a suggestion not to use String to handle passwords. Why does String pose a threat to …
Learn MoreHow to create ArrayList from an array in Java?
I have an array that is initialized like: I would like to convert this array into an object of the ArrayList class. How to create ArrayList from array in Java? Short answer: …
Learn MoreWhat are the differences between a HashMap and a Hashtable in Java?
There are several differences between HashMap and Hashtable in Java: Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones. Hashtable does not allow null keys or values. HashMap allows one null key and …
Learn MoreHow to avoid NullPointerException in Java? [Answered]
In this post, I’ll share the best answer to avoid NullPointerException in Java. How to avoid NullPointerException in Java? This to me sounds like a reasonably common problem that junior …
Learn MoreHow to convert an InputStream into a String in Java? [Answered]
Sample query: If you have a java.io.InputStream object, how should you process that object and produce a String? Suppose I have an InputStream that contains text data, and I want to convert it to a String, …
Learn MoreSubtracting two times (in 1927) is giving a strange result in Java[Answered]
Sample problem: If I run the following program, which parses two date strings referencing times 1 second apart and compares them: The output is: Why is ld4-ld3, not 1 (as I would expect …
Learn MoreHow to sort a Map by values in Java? [Answered]
Query explanation: I am relatively new to Java, and often find that I need to sort a Map<Key, Value> on the values. Since the values are not unique, I find myself converting …
Learn MoreWhat is ViewModel in MVC? [Answered]
Query explained: I am new to ASP.NET MVC. I have a problem with understanding the purpose of a ViewModel. What is a ViewModel and why do we need a ViewModel …
Learn MoreWhat is the difference between public, protected, package-private, and private in Java? [Answered]
Query: In Java, are there clear rules on when to use each of access modifiers, namely the default (package private), public, protected and private, while making class and interface and dealing with inheritance? What is the difference between …
Learn MoreNon-static variable cannot be referenced from a static context | Java [Answered]
Sample problem: I’ve written this test code: But it gives the following error: How do I get my methods to recognize my class variables? Non-static variable cannot be referenced from …
Learn More