Java Programming and the jobs that are related to this programming language are very much growing these days. There are a lot of websites and web applications that is been developed on the basis of the Java programming language. It is estimated that over 3 billion devices are developed all across the globe on the basis of the Java programing language. As the competition is very high the hiring procedure for developers roles is also very different nowadays. Here in this article are the details regarding the interview questions that the freshers can anticipate in a technical interview from the Java programming language portion.
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Java Interview Questions for Freshers
The given below are some of the fresher-level interview questions that the candidates can anticipate in an interview that is related to the Java programing language.
What is Java?
Java is the high-level, object-oriented, robust, secure programming language, platform-independent, high-performance, Multithreaded, and portable programming language. It was developed by James Gosling in June 1991. It can also be known as the platform as it provides its own JRE and API.
What are the key differences between C++ and Java?
C++ and Java both are object-oriented programming languages with some differences. The interviewer may ask the difference between the two and include this in the top Java interview questions for freshers to check their basic knowledge. The differences between C++ and Java are as follows –
| C++ | Java |
| 1) C++ is platform dependent. | 1) Java is platform-independent. |
| 2) C++ writes structural programs without using classes and objects. | 2) Java is a pure object-oriented language except for the primitive variables. |
| 3) C++ doesn’t support documentation comments. | 3) Java supports documentation comment (/**…*/) to create documentation for java code. |
| 4) C++ fully supports pointers. | 4) In Java, there is no concept of pointers. |
| 5) C++ supports multiple inheritances. | 5) Java doesn’t support multiple inheritances. |
Explain the JVM architecture?
Java Virtual Machine is the abstract machine or specification that provides a runtime environment to execute the bytecode. JVM supports Java and many other languages known as JVM languages, the program written in these languages is compiled into the bytecode and then executed by the JVM. contains key components which are classloader, memory area, execution engine, etc.
a) Classloader: It is a subsystem of JVM that loads class files. Whenever a Java program is run, it is loaded by the classloader.
b) Class Area: Class Area holds class-level data of each class file such as metadata, constant run pool, and static variables.
c) Heap: It is the runtime data that is used for allocating objects.
d) Stack: The stack is used for storing temporary variables. This component has a stack frame which is allocated one frame to each thread and when the execution of the thread is completed then that frame is also gets destroyed.
e) Registers: This component contains the address of JVM instruction which is currently being executed.
f) Native Method Stack: All the native method stacks used in the application are stored in this.
g) Execution Engine: It contains:
- A virtual processor
- An interpreter executes the instructions after reading the bytecode.
- JIT compiler, used for improving the performance due to the slow execution. It compiles a similar part of the bytecode at the same time which reduces the total time needed for compilation.
h) Java Native Interface: It provides an interface that is needed for communicating with another application developed in another language like C, C++, C# etc.
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What is the use of Classloader in Java?
Answer: A Java program is made up of a different number of custom classes and predefined classes. When a program is executed, JVM is used to load all the content of that needed class and through the use of Classloader JVM, it finds that class.
There are three types of Classloaders:
- System ClassLoader
It loads all the classes from the classpath.
- Extension ClassLoader
It loads all the classes from the extension directory.
- Bootstrap ClassLoader
It loads all the pre-defined java classes.
Which class is a superclass of all classes?
Java.lang.The object is the root class for all the java classes and we don’t need to extend it. Every other java classes fall back under the object. All the different non-primitive types including arrays are inherited directly or indirectly from this class.
What is the static keyword?
The static keyword is used with a class-level variable to make it global so all the objects will be able to share the same variable. It can also be used with methods. A static method can access only static variables of the class and invoke only a static method of the class.
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What is the difference between JDK, JRE, and JVM?
JVM: JVM is an acronym for Java Virtual Machine; it is an abstract machine that provides the runtime environment in which Java bytecode can be executed. It is a specification that specifies the working of Java Virtual Machine. Its implementation has been provided by Oracle and other companies. Its implementation is known as JRE.
JVMs are available for many hardware and software platforms (so JVM is platform-dependent). It is a runtime instance that is created when we run the Java class. There are three notions of the JVM: specification, implementation, and instance.
JRE: JRE stands for Java Runtime Environment. It is the implementation of JVM. The Java Runtime Environment is a set of software tools which are used for developing Java applications. It is used to provide the runtime environment. It is the implementation of JVM. It physically exists. It contains a set of libraries + other files that JVM uses at runtime.
JDK: JDK is an acronym for Java Development Kit. It is a software development environment which is used to develop Java applications and applets. It physically exists. It contains JRE + development tools. JDK is an implementation of any one of the below given Java Platforms released by Oracle Corporation:
- Standard Edition Java Platform
- Enterprise Edition Java Platform
- Micro Edition Java Platform
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What is the inner and anonymous inner class?
Answer: In Java, we can define a class inside a class and they are called nested classes. Any nested class which is non-static is known as the inner class. Inner classes are associated with objects of the class and they can access all the variables and methods of the outer class.
Any local inner class without any name is known as an anonymous inner class. It is defined and instantiated in a single statement. Anonymous inner classes always extend a class or implement an interface. Since an anonymous inner class doesn’t have any name, it is not possible to create its constructor.
What is the break and continue statement?
Answer: In a while or do-while loop, we use break for a statement to terminate the loop. We use a break statement in a switch statement to exit the switch case. We can also use the break statement for terminating the nested loop. The continue statement is used for skipping the current iteration of a for, while or do-while loop. We can use the break statement with a label to skip the current iteration of the outermost loop.
How many types of memory areas are allocated by JVM?
The given below are the types of memory areas that are allocated by JVM.
- Class(Method) Area: Class Area stores per-class structures such as the runtime constant pool, field, method data, and the code for methods.
- Heap: It is the runtime data area in which the memory is allocated to the objects
- Stack: Java Stack stores frames. It holds local variables and partial results, and plays a part in method invocation and return. Each thread has a private JVM stack, created at the same time as the thread. A new frame is created each time a method is invoked. A frame is destroyed when its method invocation completes.
- Program Counter Register: PC (program counter) register contains the address of the Java virtual machine instruction currently being executed.
- Native Method Stack: It contains all the native methods used in the application.
What is an interface?
Interfaces are the core part of the Java programming language used a lot in JDK, java design patterns, and most of the frameworks and tools. The interface provides a way to achieve abstraction in Java and is used to define the contract for the subclasses to implement.
The interface is a good starting point to define the type and create a top-level hierarchy in your code. In Java, a class can implement multiple interfaces, it’s better to use interfaces as a superclass in most of the cases.
What is aggregation in Java?
Aggregation is best defined as the entity reference where it represents the relationship between two classes where the aggregate class contains a reference to the class which it owns. Aggregation represents a has-a and whole/part relationship.
For example consider an aggregate class Employee stores information such as name, age, salary, and the Address class stores information such as city, state, and pin-code. Now, if the Employee class is defined to contain an Address object then it will be said that the Employee object has-a Address object. The Address object also makes up part-of Employee object – there is no employee without any address to live. Therefore, the Employee object owns the Address object.
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What is the use of the System class in Java?
This question is among the most common Java interview questions for freshers. Java System class is one of the core classes. One of the easiest ways to log information for debugging is System.out.print() method. System class is final so we can’t subclass and override its behavior through inheritance. System class doesn’t provide any public constructors, so we can’t instantiate this class and that’s why all of its methods are static. Some of the utility methods of the System class are for array copy, getting the current time, and reading environment variables.
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