1. Basic Syntax and Data Types
Java’s basic syntax is a frequent topic in interviews, including identifiers, keywords, operators, control statements, etc. In terms of data types, it is necessary to clarify the differences between primitive data types (byte, short, int, long, float, double, char, boolean) and reference data types (classes, interfaces, arrays), as well as their default values and value ranges. For example, the default value of the int type is 0, and its value range is from -2³¹ to 2³¹-1.
2. Object-Oriented Features
Encapsulation, inheritance, and polymorphism are the three major features of Java’s object-oriented programming, which are often examined in depth in interviews. Encapsulation binds data and methods for operating data together, hiding the internal implementation details of objects; inheritance allows subclasses to inherit the properties and methods of parent classes, improving code reusability; polymorphism means that the same method has different implementations on different objects, which is divided into compile-time polymorphism (overloading) and runtime polymorphism (overriding).
3. Collection Framework
The Java collection framework is a key and difficult point in interviews. It is necessary to master the implementation classes and characteristics of commonly used collections such as List, Set, and Map. For example, the difference between ArrayList and LinkedList: ArrayList is implemented based on a dynamic array, with fast query speed but slow addition and deletion; LinkedList is implemented based on a doubly linked list, with fast addition and deletion but slow query. The difference between HashMap and Hashtable is also a common interview question. HashMap is thread-unsafe and allows null keys and null values; Hashtable is thread-safe and does not allow null keys and null values.
4. Multithreading
Knowledge related to multithreading appears frequently in interviews, including ways to create threads (inheriting the Thread class, implementing the Runnable interface, using Callable and Future), thread states (new, ready, running, blocked, dead), thread synchronization mechanisms (synchronized keyword, Lock interface), and the use of thread pools. For example, the core parameters of thread pools (core thread count, maximum thread count, queue capacity, etc.) and their working principles are often asked in interviews.
5. Exception Handling
It is necessary to understand the classification of exceptions (Checked exceptions and Unchecked exceptions), the exception handling mechanism (try-catch-finally statements), and the difference between the throw and throws keywords. At the same time, one should know how to customize exceptions and how to handle exceptions reasonably in actual development to avoid swallowing exceptions or over-catching exceptions.
Feel free to leave a message if you have any questions. I’ll get back to you as soon as I see it, and I’ll share some knowledge according to your needs.