130+ Core Java Interview Questions and Answers in 2023

Cryptocurrency is the poster child of “disruptive technology” in the traditionally slow-moving finance industry. But, there are other areas where developers and software engineers must update business-as-usual in banking in order to survive. The volatile keyword tells https://remotemode.net/become-a-security-specialist/ the JVM when a variable may be modified in another threat. The volatile keyword guarantees global ordering on reads and writes to a variable. It ensures that every thread accessing a volatile field will read the variable’s  current value, instead of a cached value.

Making the constructor private will prevent the class to be instantiated. So the only possibility to access is using the Class name only. The objects referred by instance variables empObj1 and empObj2 have separate copies empNo, empName, department, and salary. However, the officePhone belongs to the class(Class Variable) and can be accessed as Employee.officePhone. Java is not considered pure Object-oriented because it supports primitive data types such as boolean, byte, char, int, float, double, long, and short.

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Depending upon the number of parameters and their corresponding types, distinguishing of the different types of constructors is done by the compiler. Whereas, an instance variable in Java, is a variable which is bounded to its object itself. These variables are declared within a class, but outside a method.

The differences between get() and load() methods are given below. @Qualifier – with @Autowired annotation to avoid confusion when multiple instances of bean type is present. You should use execute() method only when you are not sure about the type of statement else use executeQuery or executeUpdate method. Batch processing helps you to group related SQL statements into a batch and execute them instead of executing a single query. By using batch processing technique in JDBC, you can execute multiple queries which makes the performance faster. The ResultSetMetaData interface returns the information of table such as total number of columns, column name, column type etc.

What are the types of Functional interfaces?

Do While Loop is same as While loop with only difference that condition is checked after execution of block of statements. Hence in case of do while loop, statements are executed at least once. Some of the questions have not been answered here, because of the limited time I have. It means we’ll create only one instance of that static member that is shared across all instances of the class. Agile software development is a popular software development methodology; any developer knows Agile.

Java doesn’t use pointers because they are unsafe and increase the complexity of the program. Since, Java is known for its simplicity of code, adding the concept of pointers will be contradicting. Moreover, since JVM is responsible for implicit memory allocation, thus to avoid direct access to memory by the user,  pointers are discouraged in Java. It is not-thread safe and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized. HashMap allows one null key and multiple null values whereas Hashtable doesn’t allow any null key or value. HashMap is generally preferred over HashTable if thread synchronization is not needed.

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Static variable belongs to the class rather than the object. The purpose of the default constructor is to assign the default value to the objects. The java compiler creates a default constructor implicitly if there is no constructor in the class. The local variables are not initialized to any default value, neither primitives nor object references.

Today more than 10 million developers are there who are working with the Java language. Over the years, Java has improved a lot to give more to its users. To know about the history of Java, you can check out the Java version history and then start learning Java. The concept https://remotemode.net/become-a-java-developer-se-9/ of constructor overloading refers to having multiple methods in a class with their name being the same as the class name. The difference lies in the set of parameters passed to the functions. Final is used to restrict classes, variables, or methods, the final keyword.

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The method of Base class, i.e., baseMethod() is overridden in Derived class. In Test class, the reference variable b (of type Base class) refers to the instance of the Derived class. Here, Runtime polymorphism is achieved between class Base and Derived.

• In Java, all the programs will have at least one thread which is known as the main thread.
• Algorithms and data structures are the base of our job, so be prepared to dig deep into those.
• Generic methods and classes help programmers specify a single method declaration, a set of related methods, or related types with an available class declaration.
• Radek is a certified Toptal blockchain engineer particularly interested in Ethereum and smart contracts.
• System.out and System.err represent the monitor by default and thus can be used to send data or results to the monitor.
• Generally speaking, Redis was not built to achieve this.