Java basic interview questions - generics
139. What are generics in Java? What are the benefits of using generics?
(Recommended more related interview questions: java interview questions And answer )
Generics are a new feature of Java SE 1.5. The essence of generics is a parameterized type, which means that the data type being operated is specified as a parameter.
Benefits:
1. Type safety, providing type detection during compilation
2. Back and forth compatibility
3. Generalized code, the code can be updated More reuse
4. High performance. Code written in GJ (generic JAVA) can bring more type information to the Java compiler and virtual machine. This information can further optimize the Java program. provide conditions.
140, How do Java generics work? What is type erasure? How does it work?
1. Type checking: Provide type checking before generating bytecode
2. Type erasure: All type parameters are replaced with their qualified types, including classes, variables and methods ( Type erasure)
3. If type erasure conflicts with polymorphism, generate a bridge method in the subclass to solve the problem
4. If the return type of a generic method is called is erased, a cast is inserted when the method is called
Type erasure:
All type parameters are replaced with their qualified types:
For example
T->Object ? extends BaseClass->BaseClass
How it works:
Generics are implemented through type erasure. The compiler erases all type-related information at compile time, so there is no type-related information at runtime. . For example, List
141, can you pass List
For anyone who is not familiar with generics, this Java generics question may seem confusing, because at first glance String is a kind of Object, so List
List<Object> objectList; List<String> stringList; objectList = stringList; //compilation error incompatible types
142, How to prevent unchecked type warnings in Java?
If you mix generics and primitive types, such as the following code, the javac compiler of java 5 will generate Type unchecked warnings, such as
List<String> rawList = newArrayList()
Note: Hello.java uses unchecked or unsafe operations;
This kind of warning can be annotated with @SuppressWarnings("unchecked") to shield.
143, What is the difference between List
The main difference between primitive type and parameterized type
The test point of this question lies in the correct understanding of primitive types in generics. The second difference between them is that you can pass any type with parameters to the primitive type List, but you cannot pass List
144, write a generic program to implement LRU cache?
This is equivalent to an exercise for people who like Java programming. To give you a hint, LinkedHashMap can be used to implement a fixed-size LRU cache. When the LRU cache is full, it will move the oldest key-value pair out of the cache.
LinkedHashMap provides a method called removeEldestEntry(), which will be called by put() and putAll() to delete the oldest key-value pair. Of course, if you've already written a running JUnit test, you're free to write your own implementation code.
(Recommended tutorial: java course)
145, can generics be used in Array?
This may be Java generics This is the simplest interview question. Of course, the premise is that you know that Array does not actually support generics. This is why Joshua Bloch recommends using List instead of Array in the book Effective Java, because List can provide compile-time types. Security is guaranteed, while Array cannot.
146, How to write a generic method so that it can accept generic parameters and return a generic type?
编写泛型方法并不困难，你需要用泛型类型来替代原始类型，比如使用T, E or K,V等被广泛认可的类型占位符。最简单的情况下，一个泛型方法可能会像这样：
public V put(K key, V value) {
return cahe.put(key,value);
}147，C++模板和java泛型之间有何不同？
java泛型实现根植于“类型消除”这一概念。当源代码被转换为Java虚拟机字节码时，这种技术会消除参数化类型。有了Java泛型，我们可以做的事情也并没有真正改变多少；他只是让代码变得漂亮些。鉴于此，Java泛型有时也被称为“语法糖”。
这和 C++模板截然不同。在 C++中，模板本质上就是一套宏指令集，只是换了个名头，编译器会针对每种类型创建一份模板代码的副本。
由于架构设计上的差异，Java泛型和C++模板有很多不同点：
C++模板可以使用int等基本数据类型。Java则不行，必须转而使用Integer。
在Java中，可以将模板的参数类型限定为某种特定类型。
在C++中，类型参数可以实例化，但java不支持。
在Java中，类型参数不能用于静态方法(?)和变量，因为它们会被不同类型参数指定的实例共享。在C++，这些类时不同的，因此类型参数可以用于静态方法和静态变量。
在Java中，不管类型参数是什么，所有的实例变量都是同一类型。类型参数会在运行时被抹去。在C++中，类型参数不同，实例变量也不同。
相关推荐：java入门
The above is the detailed content of Java basic interview questions - generics. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
Break or return from Java 8 stream forEach?
Feb 07, 2025 pm 12:09 PM
Java 8 introduces the Stream API, providing a powerful and expressive way to process data collections. However, a common question when using Stream is: How to break or return from a forEach operation? Traditional loops allow for early interruption or return, but Stream's forEach method does not directly support this method. This article will explain the reasons and explore alternative methods for implementing premature termination in Stream processing systems. Further reading: Java Stream API improvements Understand Stream forEach The forEach method is a terminal operation that performs one operation on each element in the Stream. Its design intention is
PHP: A Key Language for Web Development
Apr 13, 2025 am 12:08 AM
PHP is a scripting language widely used on the server side, especially suitable for web development. 1.PHP can embed HTML, process HTTP requests and responses, and supports a variety of databases. 2.PHP is used to generate dynamic web content, process form data, access databases, etc., with strong community support and open source resources. 3. PHP is an interpreted language, and the execution process includes lexical analysis, grammatical analysis, compilation and execution. 4.PHP can be combined with MySQL for advanced applications such as user registration systems. 5. When debugging PHP, you can use functions such as error_reporting() and var_dump(). 6. Optimize PHP code to use caching mechanisms, optimize database queries and use built-in functions. 7
PHP vs. Python: Understanding the Differences
Apr 11, 2025 am 12:15 AM
PHP and Python each have their own advantages, and the choice should be based on project requirements. 1.PHP is suitable for web development, with simple syntax and high execution efficiency. 2. Python is suitable for data science and machine learning, with concise syntax and rich libraries.
PHP vs. Other Languages: A Comparison
Apr 13, 2025 am 12:19 AM
PHP is suitable for web development, especially in rapid development and processing dynamic content, but is not good at data science and enterprise-level applications. Compared with Python, PHP has more advantages in web development, but is not as good as Python in the field of data science; compared with Java, PHP performs worse in enterprise-level applications, but is more flexible in web development; compared with JavaScript, PHP is more concise in back-end development, but is not as good as JavaScript in front-end development.
Java Program to Find the Volume of Capsule
Feb 07, 2025 am 11:37 AM
Capsules are three-dimensional geometric figures, composed of a cylinder and a hemisphere at both ends. The volume of the capsule can be calculated by adding the volume of the cylinder and the volume of the hemisphere at both ends. This tutorial will discuss how to calculate the volume of a given capsule in Java using different methods. Capsule volume formula The formula for capsule volume is as follows: Capsule volume = Cylindrical volume Volume Two hemisphere volume in, r: The radius of the hemisphere. h: The height of the cylinder (excluding the hemisphere). Example 1 enter Radius = 5 units Height = 10 units Output Volume = 1570.8 cubic units explain Calculate volume using formula: Volume = π × r2 × h (4
PHP vs. Python: Core Features and Functionality
Apr 13, 2025 am 12:16 AM
PHP and Python each have their own advantages and are suitable for different scenarios. 1.PHP is suitable for web development and provides built-in web servers and rich function libraries. 2. Python is suitable for data science and machine learning, with concise syntax and a powerful standard library. When choosing, it should be decided based on project requirements.
Create the Future: Java Programming for Absolute Beginners
Oct 13, 2024 pm 01:32 PM
Java is a popular programming language that can be learned by both beginners and experienced developers. This tutorial starts with basic concepts and progresses through advanced topics. After installing the Java Development Kit, you can practice programming by creating a simple "Hello, World!" program. After you understand the code, use the command prompt to compile and run the program, and "Hello, World!" will be output on the console. Learning Java starts your programming journey, and as your mastery deepens, you can create more complex applications.
PHP: The Foundation of Many Websites
Apr 13, 2025 am 12:07 AM
The reasons why PHP is the preferred technology stack for many websites include its ease of use, strong community support, and widespread use. 1) Easy to learn and use, suitable for beginners. 2) Have a huge developer community and rich resources. 3) Widely used in WordPress, Drupal and other platforms. 4) Integrate tightly with web servers to simplify development deployment.
