1. What is Java?
Answer: Java is a high-level, object-oriented, and platform-independent programming language. It is known for its “Write Once, Run Anywhere” capability, meaning Java code can run on any platform that has a Java Virtual Machine (JVM).
2. What are the main features of Java?
Answer: Java’s main features include:
- Object-Oriented: Java follows an object-oriented programming (OOP) paradigm.
- Platform-Independent: Java code can run on any platform with a JVM.
- Simple and Easy to Learn: Java has a straightforward syntax.
- Multithreading: It supports concurrent execution of threads.
- Robust: Java has strong memory management and exception handling.
- Secure: Java includes security features like classloaders and bytecode verification.
- Portable: Java bytecode is portable across different systems.
- Dynamic: It supports dynamic memory allocation and garbage collection.
3. What is the difference between JDK, JRE, and JVM?
Answer:
- JDK (Java Development Kit): JDK is a software package used for developing Java applications. It includes the Java compiler, libraries, and tools.
- JRE (Java Runtime Environment): JRE is used for running Java applications. It includes the JVM and libraries required to run Java programs.
- JVM (Java Virtual Machine): JVM is the runtime environment where Java bytecode is executed. It interprets and executes Java code.
4. Explain the main components of Java.
Answer: Java has three main components:
- JVM (Java Virtual Machine): It executes Java bytecode.
- JRE (Java Runtime Environment): It provides the runtime environment for Java applications.
- JDK (Java Development Kit): It includes tools and libraries for Java development.
5. What is the difference between an object and a class in Java?
Answer:
- A class is a blueprint or template for creating objects.
- An object is an instance of a class, representing a real-world entity. Objects have state and behavior defined by the class.
6. How do you declare a variable in Java, and what are the data types available?
Answer: Variables are declared with a data type in Java. For example:
javaCopy code
int age = 25; String name = "John";
Common data types include int, double, char, boolean, and String.
7. Explain the difference between ‘==’ and ‘.equals()’ in Java for comparing objects.
Answer:
- ‘==’ is used to compare object references. It checks if two objects reference the same memory location.
.equals()is a method used to compare the content or values of objects. It should be overridden in classes where value comparison makes sense.
8. What is the purpose of the ‘static’ keyword in Java?
Answer: The ‘static’ keyword is used to define static variables and methods. Static members belong to the class itself rather than instances of the class. They can be accessed using the class name.
9. What is an exception in Java, and how do you handle exceptions?
Answer: An exception is an abnormal event or error that occurs during program execution. To handle exceptions, Java provides try-catch blocks. Code that might throw an exception is placed in the try block, and the catch block handles the exception by specifying the action to take if an exception occurs.
10. What is the ‘main’ method in Java, and why is it important?
Answer: The ‘main’ method is the entry point for Java applications. It is required for a Java program to run. The JVM calls the ‘main’ method to start the execution of the program.
