Java is a widely used programming language with the characteristics of cross-platform, security, portability, multi-threading, etc., so it is widely used in various software development fields. When learning Java programming, there are some key concepts and codes that Java beginners must master.
1. Basic data types and variables
The basic data types of Java include byte, short, int, long, float, double, boolean and char. These data types are Java The basics of programming, you need to be familiar with their uses and features. In addition, learn how to declare, assign, and access variables.
public class Main {
public static void main(String[] args) {
byte b = 1;
short s = 2;
int i = 3;
long l = 4L;
float f = 5.0f;
double d = 6.0;
boolean bool = true;
char c = 'A';
}
}2. Operators and expressions
Operators in Java include arithmetic operators, relational operators, logical operators, assignment operators, etc. Familiarity with the usage and precedence of these operators is fundamental to writing Java code.
public class Main {
public static void main(String[] args) {
int a = 10;
int b = 20;
int c = a + b;
int d = a * b;
int e = a > b ? 1 : 0;
}
}3. Control statements
Control statements are statements used to control the execution flow of the program, including conditional statements (if, else, switch), loop statements (for , while, do-while) and jump statements (break, continue, return), etc. Mastering the use of these control statements can help you write more complex programs.
public class Main {
public static void main(String[] args) {
int i = 1;
while (i <= 10) {
System.out.println(i);
i++;
}
}
}4, Arrays and Strings
An array in Java is a container used to store multiple data of the same type. Learning how to declare arrays, create arrays, access array elements, and manipulate arrays is an essential skill in Java programming. Also, the string is Another important data type in Java requires mastering the operation methods and techniques of strings.
public class Main {
public static void main(String[] args) {
int[] arr = {1, 2, 3, 4, 5};
for (int i = 0; i < arr.length; i++) {
System.out.println(arr[i]);
}
String str = "Hello, World!";
System.out.println(str.length());
}
}5. Object-oriented programming
Java is an object-oriented programming language, so understanding the basic concepts and principles of object-oriented programming is a must for Java beginners class. These concepts include classes, objects, inheritance, encapsulation, polymorphism, etc.
public class Main {
public static void main(String[] args) {
Animal dog = new Animal();
dog.eat();
Animal cat = new Cat();
cat.eat();
}
}
class Animal {
public void eat() {
System.out.println("Animal eating...");
}
}
class Cat extends Animal {
public void eat() {
System.out.println("Cat eating...");
}
}6. Exception handling
In Java programming, exception handling is an important link. Learning how to handle exceptions can improve the robustness of your program. Exception handling mechanisms in Java include try-catch-finally statement, throws keyword, custom exception class, etc.
public class Main {
public static void main(String[] args) {
try {
int[] arr = new int[10];
for (int i = 0; i < arr.length; i++) {
arr[i] = 10;
}
} catch (ArrayIndexOutOfBoundsException e) {
System.out.println("Array index out of bounds");
}
}The above is the detailed content of Getting started with must-memorize code in java. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
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
css dark mode toggle example
Jul 30, 2025 am 05:28 AM
First, use JavaScript to obtain the user system preferences and locally stored theme settings, and initialize the page theme; 1. The HTML structure contains a button to trigger topic switching; 2. CSS uses: root to define bright theme variables, .dark-mode class defines dark theme variables, and applies these variables through var(); 3. JavaScript detects prefers-color-scheme and reads localStorage to determine the initial theme; 4. Switch the dark-mode class on the html element when clicking the button, and saves the current state to localStorage; 5. All color changes are accompanied by 0.3 seconds transition animation to enhance the user
python parse date string example
Jul 30, 2025 am 03:32 AM
Use datetime.strptime() to convert date strings into datetime object. 1. Basic usage: parse "2023-10-05" as datetime object through "%Y-%m-%d"; 2. Supports multiple formats such as "%m/%d/%Y" to parse American dates, "%d/%m/%Y" to parse British dates, "%b%d,%Y%I:%M%p" to parse time with AM/PM; 3. Use dateutil.parser.parse() to automatically infer unknown formats; 4. Use .d
css dropdown menu example
Jul 30, 2025 am 05:36 AM
Yes, a common CSS drop-down menu can be implemented through pure HTML and CSS without JavaScript. 1. Use nested ul and li to build a menu structure; 2. Use the:hover pseudo-class to control the display and hiding of pull-down content; 3. Set position:relative for parent li, and the submenu is positioned using position:absolute; 4. The submenu defaults to display:none, which becomes display:block when hovered; 5. Multi-level pull-down can be achieved through nesting, combined with transition, and add fade-in animations, and adapted to mobile terminals with media queries. The entire solution is simple and does not require JavaScript support, which is suitable for large
VSCode settings.json location
Aug 01, 2025 am 06:12 AM
The settings.json file is located in the user-level or workspace-level path and is used to customize VSCode settings. 1. User-level path: Windows is C:\Users\\AppData\Roaming\Code\User\settings.json, macOS is /Users//Library/ApplicationSupport/Code/User/settings.json, Linux is /home//.config/Code/User/settings.json; 2. Workspace-level path: .vscode/settings in the project root directory
css full page layout example
Jul 30, 2025 am 05:39 AM
Full screen layout can be achieved using Flexbox or Grid. The core is to make the minimum height of the page the viewport height (min-height:100vh); 2. Use flex:1 or grid-template-rows:auto1frauto to make the content area occupy the remaining space; 3. Set box-sizing:border-box to ensure that the margin does not exceed the container; 4. Optimize the mobile experience with responsive media query; this solution is compatible with good structure and is suitable for login pages, dashboards and other scenarios, and finally realizes a full screen page layout with vertical centering and full viewport.
How to handle transactions in Java with JDBC?
Aug 02, 2025 pm 12:29 PM
To correctly handle JDBC transactions, you must first turn off the automatic commit mode, then perform multiple operations, and finally commit or rollback according to the results; 1. Call conn.setAutoCommit(false) to start the transaction; 2. Execute multiple SQL operations, such as INSERT and UPDATE; 3. Call conn.commit() if all operations are successful, and call conn.rollback() if an exception occurs to ensure data consistency; at the same time, try-with-resources should be used to manage resources, properly handle exceptions and close connections to avoid connection leakage; in addition, it is recommended to use connection pools and set save points to achieve partial rollback, and keep transactions as short as possible to improve performance.
Full-Stack Web Development with Java, Spring Boot, and React
Jul 31, 2025 am 03:33 AM
Selecting the Java SpringBoot React technology stack can build stable and efficient full-stack web applications, suitable for small and medium-sized to large enterprise-level systems. 2. The backend uses SpringBoot to quickly build RESTfulAPI. The core components include SpringWeb, SpringDataJPA, SpringSecurity, Lombok and Swagger. The front-end separation is achieved through @RestController returning JSON data. 3. The front-end uses React (in conjunction with Vite or CreateReactApp) to develop a responsive interface, uses Axios to call the back-end API, and ReactRouter
Java Performance Optimization and Profiling Techniques
Jul 31, 2025 am 03:58 AM
Use performance analysis tools to locate bottlenecks, use VisualVM or JProfiler in the development and testing stage, and give priority to Async-Profiler in the production environment; 2. Reduce object creation, reuse objects, use StringBuilder to replace string splicing, and select appropriate GC strategies; 3. Optimize collection usage, select and preset initial capacity according to the scene; 4. Optimize concurrency, use concurrent collections, reduce lock granularity, and set thread pool reasonably; 5. Tune JVM parameters, set reasonable heap size and low-latency garbage collector and enable GC logs; 6. Avoid reflection at the code level, replace wrapper classes with basic types, delay initialization, and use final and static; 7. Continuous performance testing and monitoring, combined with JMH
