理解Java中的static和final：内存分配与访问特性

static
final.
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"Java中的'static'和'final'是两个重要的关键字，它们各自有着独特的用途和行为特性。首先，'static'用来标记成员变量和成员方法为全局或静态，这意味着它们与类的实例无关，而是类本身的一部分。静态变量在类加载时就已经初始化，并且在整个程序运行期间只有一份拷贝，这在内存管理上具有节省空间的优势。静态方法同样无需创建类的实例即可被访问，可以通过类名直接调用，这使得它们在需要类级操作而非实例操作的场景下非常有用。 被static修饰的变量通常被称为类变量，如`ClassVar`，可以通过`ClassName.ClassVar`的形式直接访问。然而，尽管静态变量可以通过类名访问，但建议仅在确实需要全局共享的情况下使用，避免在实例方法中直接操作，以保持代码清晰和避免潜在的并发问题。 另一方面，'final'用于修饰变量或方法，表示其值不可变或方法不可重写。对于变量，一旦赋值，就不能再更改（常量）；对于方法，表示该方法不能有任何子类重写。这对于提高代码的安全性和确定性有很大帮助，尤其是在多态和继承的上下文中。 值得注意的是，静态变量虽然可以被private修饰，但这并不意味着它们完全隐藏起来，只是限制了外部类的直接访问，只能在类的内部访问。同时，静态代码块在类加载时执行，提供了初始化静态资源的便捷时机。 理解和掌握'static'和'final'的关键在于它们如何影响代码的生命周期、内存管理和可重用性。在编写Java代码时，合理运用这两个特性可以提升代码的组织和性能，避免不必要的复杂性。"

Rails Recipes Final.pdf

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### Rails Recipes Final.pdf 知识点解析 #### 标题：Rails Recipes Final.pdf - **核心概念**：本书名为《Rails Recipes》，旨在提供一系列针对Ruby on Rails开发过程中的实用技巧和解决方案。 #### 描述：...

Java 1.Conclude the usage of the keyword final and static. 2.Introduction of Parent Delegation Model

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1. The keyword final is used to declare a constant variable, which means the value of the variable cannot be changed once it is assigned. It can also be used to make a method or class immutable, which...

All method binding in Java uses late binding unless the method is static or final (private methods are implicitly final).

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In Java, all non-static and non-final methods use late binding (also known as dynamic binding or run-time binding) by default. This means that the method implementation to be called is decided at ...

Java Methods-Java Syntax and Style.ppt

2023-09-05 上传
* 存储修饰符：`public`、`private`、`static`、`final` 等。 * 控制语句：`if`、`else`、`switch`、`while`、`for` 等。 * 内置常量：`true`、`false`、`null` 等。 总共有约 50 个保留字。 风格 Java 方法的...

package XXLChess; //import org.reflections.Reflections; //import org.reflections.scanners.Scanners; import processing.core.PApplet; import processing.core.PImage; import processing.data.JSONObject; import processing.data.JSONArray; import processing.core.PFont; import processing.event.MouseEvent; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.TimeUnit; import java.awt.Font; import java.io.*; import java.util.*; public class App extends PApplet { public static final int SPRITESIZE = 480; public static final int CELLSIZE = 48; public static final int SIDEBAR = 120; public static final int BOARD_WIDTH = 14; public static int WIDTH = CELLSIZE*BOARD_WIDTH+SIDEBAR; public static int HEIGHT = BOARD_WIDTH*CELLSIZE; public static final int FPS = 60; public String configPath; public App() { this.configPath = "config.json"; } /** * Initialise the setting of the window size. */ public void settings() { size(WIDTH, HEIGHT); } /** * Load all resources such as images. Initialise the elements such as the player, enemies and map elements. */ public void setup() { frameRate(FPS); // Load images during setup // PImage spr = loadImage("src/main/resources/XXLChess/"+...); // load config JSONObject conf = loadJSONObject(new File(this.configPath)); } /** * Receive key pressed signal from the keyboard. */ public void keyPressed(){ } /** * Receive key released signal from the keyboard. */ public void keyReleased(){ } @Override public void mouseClicked(MouseEvent e) { } @Override public void mouseDragged(MouseEvent e) { } /** * Draw all elements in the game by current frame. */ public void draw() { } // Add any additional methods or attributes you want. Please put classes in different files. public static void main(String[] args) { PApplet.main("XXLChess.App"); } }

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这是一个 Java 程序，使用 Processing 库进行可视化。它创建了一个名为 App 的类，该类具有以下属性： - SPRITESIZE：棋子的尺寸 - CELLSIZE：棋盘格子的尺寸 - SIDEBAR：侧边栏的宽度 - BOARD_WIDTH：棋盘的宽度 ...

package com.bolt.gateway.config; import com.bolt.gateway.handler.HystrixFallbackHandler; import com.bolt.gateway.props.AuthProperties; import com.bolt.gateway.props.RouteProperties; import lombok.AllArgsConstructor; import lombok.extern.slf4j.Slf4j; import org.springframework.boot.context.properties.EnableConfigurationProperties; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.http.HttpHeaders; import org.springframework.http.HttpMethod; import org.springframework.http.HttpStatus; import org.springframework.http.MediaType; import org.springframework.http.server.reactive.ServerHttpRequest; import org.springframework.http.server.reactive.ServerHttpResponse; import org.springframework.web.cors.reactive.CorsUtils; import org.springframework.web.filter.reactive.HiddenHttpMethodFilter; import org.springframework.web.reactive.function.server.RequestPredicates; import org.springframework.web.reactive.function.server.RouterFunction; import org.springframework.web.reactive.function.server.RouterFunctions; import org.springframework.web.server.ServerWebExchange; import org.springframework.web.server.WebFilter; import org.springframework.web.server.WebFilterChain; import reactor.core.publisher.Mono; /** * 路由配置信息 * * @author arch_group */ @Slf4j @Configuration @AllArgsConstructor @EnableConfigurationProperties({RouteProperties.class, AuthProperties.class}) public class RouterFunctionConfiguration { /** * 这里为支持的请求头，如果有自定义的header字段请自己添加 */ private static final String ALLOWED_HEADERS = "x-requested-with, zkpt-ks-auth, Content-Type, Authorization, credential, X-XSRF-TOKEN, token, username, client"; private static final String ALLOWED_METHODS = "*"; private static final String ALLOWED_ORIGIN = "*"; private static final String ALLOWED_EXPOSE = "*"; private static final String MAX_AGE = "18000L"; private final HystrixFallbackHandler hystrixFallbackHandler; @Bean public WebFilter corsFilter() { return (ServerWebExchange ctx, WebFilterChain chain) -> { ServerHttpRequest request = ctx.getRequest(); if (CorsUtils.isCorsRequest(request)) { ServerHttpResponse response = ctx.getResponse(); HttpHeaders headers = response.getHeaders(); headers.add("Access-Control-Allow-Headers", ALLOWED_HEADERS); headers.add("Access-Control-Allow-Methods", ALLOWED_METHODS); headers.add("Access-Control-Allow-Origin", ALLOWED_ORIGIN); headers.add("Access-Control-Expose-Headers", ALLOWED_EXPOSE); headers.add("Access-Control-Max-Age", MAX_AGE); headers.add("Access-Control-Allow-Credentials", "true"); if (request.getMethod() == HttpMethod.OPTIONS) { response.setStatusCode(HttpStatus.OK); return Mono.empty(); } } return chain.filter(ctx); }; } @Bean public RouterFunction routerFunction() { return RouterFunctions.route( RequestPredicates.path("/fallback") .and(RequestPredicates.accept(MediaType.TEXT_PLAIN)), hystrixFallbackHandler); } /** * 解决springboot2.0.5版本出现的 Only one connection receive subscriber allowed. * 参考：https://github.com/spring-cloud/spring-cloud-gateway/issues/541 */ @Bean public HiddenHttpMethodFilter hiddenHttpMethodFilter() { return new HiddenHttpMethodFilter() { @Override public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) { return chain.filter(exchange); } }; } }

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这是一个Spring Cloud Gateway的路由配置类。它使用了函数式编程风格来定义路由规则。 在这个类中，主要做了以下几件事情： 1. 配置跨域请求的过滤器(corsFilter)：当请求的Origin与服务端的地址不一致时，浏览器会...

private final static sting drivername

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This declares a private, static, and final string variable named `DRIVER_NAME`, which is initialized with the value `"com.mysql.jdbc.Driver"`. The `static` keyword means that the variable belongs to ...

public class LoginBean { private String username; private String password; // 数据库连接设置 private static final String DB_URL = "jdbc:mysql://localhost:3306/test?serverTimezone=Asia/Shanghai"; private static final String DB_USERNAME = "root"; private static final String DB_PASSWORD = "123456"; public LoginBean(String username, String password) { this.username = username; this.password = password; } public boolean validate() { try { // 加载 MySQL 驱动 Class.forName("com.mysql.cj.jdbc.Driver"); // 连接数据库 Connection conn = DriverManager.getConnection(DB_URL, DB_USERNAME, DB_PASSWORD); String query = "SELECT * FROM user WHERE username = ? AND password = ?"; PreparedStatement stmt = conn.prepareStatement(query); stmt.setString(1, username); stmt.setString(2, password); ResultSet rs = stmt.executeQuery(); if (rs.next()) { return true; // 用户名和密码匹配 } rs.close(); stmt.close(); conn.close(); } catch (Exception e) { System.err.println("连接数据库时出现异常：" + e.getMessage()); e.printStackTrace(); } return false; // 登录失败 }public class LoginAction extends ActionSupport { private String username; private String password; private LoginBean loginBean; // Getter 和 Setter 方法 public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } // 登录操作 public String execute() { loginBean = new LoginBean(username, password); if (loginBean.validate()) { return "SUCCESS"; // 登录成功 } else { return "LOGIN"; }

2025-03-10 上传
AND password=?"; try (Connection conn = dataSource.getConnection(); PreparedStatement pstmt = conn.prepareStatement(sql)) { pstmt.setString(1, userName); pstmt.setString(2, PasswordUtil.hash...

The serializable class does not declare a static final serialVersionUID field of type long

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To fix this warning, you should define a static final serialVersionUID field in the serializable class. The value of this field should be a long integer, and it should be unique for each version of ...

public static final AppFilter FILTER_DOWNLOADED_AND_LAUNCHER = new AppFilter() { @Override public void init() { } @Override public boolean filterApp(AppEntry entry) { if (AppUtils.isInstant(entry.info)) { return false; } else if (hasFlag(entry.info.flags, ApplicationInfo.FLAG_UPDATED_SYSTEM_APP)) { return true; } else if (!hasFlag(entry.info.flags, ApplicationInfo.FLAG_SYSTEM)) { return true; } else if (entry.hasLauncherEntry) { return true; } else if (hasFlag(entry.info.flags, ApplicationInfo.FLAG_SYSTEM) && entry.isHomeApp) { return true; } return false; } };详解

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这段代码定义了一个名为FILTER_DOWNLOADED_AND_LAUNCHER的静态常量，类型为AppFilter。它的值是一个匿名内部类的实例，实现了AppFilter接口中的两个方法init和filterApp。 init方法在实例化时不会被调用，它的作用...
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