Generic Classes in Java
Java Generics was introduced to deal with type-safe objects. It makes the code stable.Java Generics methods and classes, enables programmer with a single method declaration, a set of related methods, a set of related...
Loop and Break
Singleton Invalidated by Multithreading
Singleton will work properly in multithreaded environment only if eager instantiation has been done because in this case instance creation will happen at the time of class loading only. But for Lazy instantiation we...
Singleton Invalidated by Serialization
When we serialize an object and deserialize it again there are different hash code values generated as shown in the example below. So our Singleton principle breaks in case of object serialization/deserialization. Output How...
Singleton Invalidated by Clone
If we try to make instance by cloning it, the generated hash code of cloned copy doesn’t match with the actual object so it also violates the Singleton principle. Example Output How to fix:...
Singleton Invalidated by Reflection
Using reflection we can set the private constructor to become accessible at runtime as shown in the example below. Example Output In above output we are seeing first two objects are assigned same hashcode,...
Singleton Design Pattern
Sometimes it’s important for some classes to have exactly one instance. There are many objects we only need one instance of them and if we, instantiate more than one, we’ll run into all sorts...
Using Comparators to sort objects in Java
Comparator interface is used to order the objects of user-defined classes. A comparator object is capable of comparing two objects of two different classes. Following comparator will sort by ID Example Output You can...
Use comparable to sort first by 1st field and then second field in Java
In order to sort first by ID and if the Id’s are same then sort by name. Please follow the code Example Output
Builder Design Pattern in Java
Builder pattern was introduced to solve some of the problems with Factory and Abstract Factory design patterns when the Object contains a lot of attributes. There are three major issues with Factory and Abstract...
Shallow vs Deep copy in Java
When creating copies of arrays or objects one can make a deep copy or a shallow copy. Shallow Copy Output In above example we have changed the value of arr1[2] to 10. Since it’s...
Efficiently removing elements while iterating a collection in Java
One of the common problem while removing elements from an ArrayList in Java is the ConcurrentModificationException. If you use classical for loop with the index or enhanced for loop and try to remove an...
Spring Boot CRUD REST API with MySql
Here is an example of the REST API using spring boot with MySql as the database. We have used a single table of Employee, with custom exception handler to give users readable error messages....
Use your class as a bean in Spring Boot
Depending on your needs, you can either leverage @ComponentScan to automatically detect your class and have an instance created, use it together with @Autowired and @Value to get dependencies or properties injected, or you...
Sort List of Collections in Java using Comparable interface
A comparable object is capable of comparing itself with another object. The class itself must implements the java.lang.Comparable interface to compare its instances. Example Output In the above example, ID 5 is same for...
Iterate around an ArrayList using Iterator
Example below shows how to iterate around an ArrayList. Example Output
What is the use of equals method in Java?
Equals method is used when we compare two objects. Default implementation of equals method is defined in Object class. The implementation is similar to == operator. Two object references are equal only if they...