Java interview FAQs and answers

As a common programming language, Java is widely used in the IT industry and has become one of the important skills in recruitment for many companies. In interviews for Java development positions, interviewers often ask some common Java questions to examine the applicant's Java programming level. This article will list several common Java interview questions and their answers for the reference of candidates.

1. What is Java Virtual Machine?

Answer: The Java Virtual Machine (JVM) is a virtual computer that can execute Java bytecode. It is one of the core components of the Java platform and is responsible for the running of Java programs. Java programs will generate bytecode after compilation. The JVM will convert the bytecode into instructions that the machine can understand, and then run the program.

2. What is the difference between static variables and instance variables in Java?

Answer: Static variables refer to variables modified with the static keyword. They are member variables of the class, not the member variables of the object. Static variables are allocated memory when the class is loaded and exist throughout the execution of the program. Instance variables refer to variables that are not modified with the static keyword and are member variables of the object. Each object has a copy of the instance variables, independent of each other.

3. What is the difference between String and StringBuilder in Java?

Answer: String is a string type in Java. It is immutable, that is, once created, it will not be changed. Every time a String is modified, a new String object is created. StringBuilder is a mutable string type that can change its own value without creating a new object. Therefore, in scenarios that require a large number of string operations (such as concatenating strings), using StringBuilder is more efficient than using String.

4. What is polymorphism in Java?

Answer: Polymorphism is a concept in Java. It refers to objects of the same parent class that will show different behaviors in different situations. By inheriting and implementing interfaces, subclasses in Java can override the methods of the parent class and also implement the methods of the parent class. When the program is executed, it is decided which specific implementation to execute based on the actual type of the object.

5. What are the exceptions in Java? When should you use exceptions?

Answer: Exceptions in Java include runtime exceptions (RuntimeException), non-runtime exceptions (non-RuntimeException), and errors (Error). Exceptions should be used when unexpected errors may occur. For example, when a user enters illegal data, you can use exceptions to handle it. When writing reliable programs, exception handling and capturing should be fully considered to ensure the robustness and maintainability of the program.

Summary:

The above questions are all common questions in Java interviews. I hope the answers in this article can help readers who are preparing for Java interviews. It should be noted that the interview not only tests knowledge level, but also pays attention to practical ability and problem-solving ability. Therefore, when answering questions, it is recommended to combine practical experience and give appropriate examples to highlight your own advantages.

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