Java Interviews: Tips and Practice
In today's IT industry, Java has become a very popular programming language. It has attracted countless developers because of its cross-platform, object-oriented, and high security features. However, mastering Java is not an easy task, especially during the interview process. This article will give you some tips and practical experience about Java interviewing to help you stand out in the interview.
1. Basic knowledge of Java
1. Features of Java
Java is an object-oriented programming language with the following characteristics:
- Cross-platform: Java programs can run on different operating systems, just write the code once.
- Object-oriented: Java supports object-oriented features such as encapsulation, inheritance, and polymorphism.
- Security: Java has strict type checking and security mechanisms to prevent memory leaks and other security issues.
- High performance: Java adopts garbage collection mechanism to automatically manage memory and improve the operating efficiency of the program.
2. Basic data types in Java
Java has 8 basic data types, which are divided into four categories:
- Integer type: byte (8 bits), short (16 bits), int (32 bits), long (64 bits).
- Floating point type: float (32 bits), double (64 bits).
- Character type: char (16 bits).
- Boolean: boolean(true/false).
3. Operators in Java
Java supports a variety of operators, including arithmetic operators, relational operators, logical operators, bitwise operators, assignment operators, conditional operators, etc.
4. Java conditional statement
There are three kinds of conditional statements in Java: if-else, switch-case, and the ternary operator (?:).
5. Java loop statement
There are two kinds of loop statements in Java: for loop and while loop. In addition, there is an enhanced for loop (for-each loop).
6. Java methods
A method is a block of code with a specific function that can be called by other methods. Methods in Java have the following characteristics:
- Access modifiers: public, private, protected, default (do not write).
- Return value type: void (no return value), basic data type, reference data type or custom class.
- Method name: follow the camel case naming convention.
- Parameter list: There can be multiple parameters, each parameter is separated by a comma. Parameters can have a name and type, or be omitted.
- Method body: Surrounded by curly braces {}, it contains a series of statements.
7. Java exception handling
Exception handling in Java mainly includes three keywords: try-catch-finally. When an exception occurs in the program, you can use the try-catch statement to catch and handle the exception. The code in the finally block executes regardless of whether an exception occurs.
2. Java collection framework
1. List interface
The List interface is one of the most commonly used interfaces in the Java collection framework, representing an ordered list. Commonly used implementation classes are ArrayList, LinkedList and Vector.
2. Set interface
The Set interface represents an unordered and non-repeated collection of elements. The commonly used implementation classes are HashSet, TreeSet and LinkedHashSet.
3. Map interface
The Map interface represents a mapping relationship of key-value pairs. The commonly used implementation classes are HashMap, TreeMap and LinkedHashMap.
4. Features of Java collection framework
- Inheritance: All interfaces of the Java collection framework inherit from the Collection interface.
- Polymorphism: Collection objects can be directly manipulated through the interface without caring about the specific implementation class.
- Performance optimization: The design of the Java collection framework fully considers performance optimization, such as using caches and reducing object creation.
- Generic support: The Java collection framework supports generics, which can improve code reusability and type safety.
3. Java multi-threaded programming
1. The concept and characteristics of threads
A thread is a unit of program execution, and the resources of the process are shared between threads. Characteristics of threads include independence, lightweight, and synchronization.
2. How to create and start a Java thread
There are mainly the following ways to create and start Java threads:
- Inherit the Thread class and override the run() method; call the start() method to start the thread after the subclass is instantiated.
- Implement the Runnable interface and implement the run() method; pass in the Runnable instance to start the thread through the constructor of the Thread class. This approach is recommended because it avoids the limitations of single inheritance.