50个JAVA常见代码大全：学完这篇从Java小白到架构师

Java，作为一门流行多年的编程语言，始终占据着软件开发领域的重要位置。无论是初学者还是经验丰富的程序员，掌握Java中常见的代码和概念都是至关重要的。本文将列出50个Java常用代码示例，并提供相应解释，助力你从Java小白成长为架构师。

基础语法

1. Hello World

public class HelloWorld {     public static void main(String[] args) {         System.out.println("Hello, World!");     } } 

2. 数据类型

int a = 100; float b = 5.25f; double c = 5.25; boolean d = true; char e = 'A'; String f = "Hello"; 

3. 条件判断

if (a > b) {     // 条件成立时执行 } else if (a == b) {     // 另一个条件 } else {     // 条件都不成立时执行 } 

4. 循环结构

for循环

for (int i = 0; i < 10; i++) {     System.out.println("i: " + i); } 

while循环

int i = 0; while (i < 10) {     System.out.println("i: " + i);     i++; } 

do-while循环

int i = 0; do {     System.out.println("i: " + i);     i++; } while (i < 10); 

5. 数组

int[] arr = new int[5]; arr[0] = 1; arr[1] = 2; // ... int[] arr2 = {1, 2, 3, 4, 5}; 

6. 方法定义与调用

public static int add(int a, int b) {     return a + b; } int sum = add(5, 3); // 调用方法 

面向对象编程

7. 类与对象

public class Dog {     String name;      public void bark() {         System.out.println(name + " says: Bark!");     } }  Dog myDog = new Dog(); myDog.name = "Rex"; myDog.bark(); 

8. 构造方法

public class User {     String name;      public User(String newName) {         name = newName;     } }  User user = new User("Alice"); 

9. 继承

public class Animal {     void eat() {         System.out.println("This animal eats food.");     } }  public class Dog extends Animal {     void bark() {         System.out.println("The dog barks.");     } }  Dog dog = new Dog(); dog.eat(); // 继承自Animal dog.bark(); 

10. 接口

public interface Animal {     void eat(); }  public class Dog implements Animal {     public void eat() {         System.out.println("The dog eats.");     } }  Dog dog = new Dog(); dog.eat(); 

11. 抽象类

public abstract class Animal {     abstract void eat(); }  public class Dog extends Animal {     void eat() {         System.out.println("The dog eats.");     } }  Animal dog = new Dog(); dog.eat(); 

12. 方法重载

public class Calculator {     int add(int a, int b) {         return a + b;    ```java     double add(double a, double b) {         return a + b;     }      int add(int a, int b, int c) {         return a + b + c;     } }  Calculator calc = new Calculator(); calc.add(5, 3); // 调用第一个方法 calc.add(5.0, 3.0); // 调用第二个方法 calc.add(5, 3, 2); // 调用第三个方法 

13. 方法重写

public class Animal {     void makeSound() {         System.out.println("Some sound");     } }  public class Dog extends Animal {     @Override     void makeSound() {         System.out.println("Bark");     } }  Animal myDog = new Dog(); myDog.makeSound(); // 输出 "Bark" 

14. 多态

public class Animal {     void makeSound() {         System.out.println("Some generic sound");     } }  public class Dog extends Animal {     @Override     void makeSound() {         System.out.println("Bark");     } }  public class Cat extends Animal {     @Override     void makeSound() {         System.out.println("Meow");     } }  Animal myAnimal = new Dog(); myAnimal.makeSound(); // Bark myAnimal = new Cat(); myAnimal.makeSound(); // Meow 

15. 封装

public class Account {     private double balance;      public Account(double initialBalance) {         if(initialBalance > 0) {             balance = initialBalance;         }     }      public void deposit(double amount) {         if(amount > 0) {             balance += amount;         }     }      public void withdraw(double amount) {         if(amount <= balance) {             balance -= amount;         }     }      public double getBalance() {         return balance;     } }  Account myAccount = new Account(50); myAccount.deposit(150); myAccount.withdraw(75); System.out.println(myAccount.getBalance()); // 应输出：125.0 

16. 静态变量和方法

public class MathUtils {     public static final double PI = 3.14159;      public static double add(double a, double b) {         return a + b;     }      public static double subtract(double a, double b) {         return a - b;     }      public static double multiply(double a, double b) {         return a * b;     } }  double circumference = MathUtils.PI * 2 * 5; System.out.println(circumference); // 打印圆的周长 

17. 内部类

public class OuterClass {     private String msg = "Hello";      class InnerClass {         void display() {             System.out.println(msg);         }     }      public void printMessage() {         InnerClass inner = new InnerClass();         inner.display();     } }  OuterClass outer = new OuterClass(); outer.printMessage(); // 输出 "Hello" 

18. 匿名类

abstract class SaleTodayOnly {     abstract int dollarsOff(); }  public class Store {     public SaleTodayOnly sale = new SaleTodayOnly() {         int dollarsOff() {             return 3;         }     }; }  Store store = new Store(); System.out.println(store.sale.dollarsOff()); // 应输出3 

高级编程概念

19. 泛型

public class Box {     private T t;      public void set(T t) {         this.t = t;     }      public T get() {         return t;     } }  Box integerBox = new Box<>(); integerBox.set(10); System.out.println(integerBox.get()); // 应输出：10 

20. 集合框架

ArrayList

import java.util.ArrayList;  ArrayList list = new ArrayList<>(); list.add("Java"); list.add("Python"); list.add("C++"); System.out```java .println(list); // 应输出：[Java, Python, C++] 

HashMap

import java.util.HashMap;  HashMap map = new HashMap<>(); map.put("Apple", 1); map.put("Banana", 2); map.put("Cherry", 3); System.out.println(map.get("Apple")); // 应输出：1 

21. 异常处理

try {     int result = 10 / 0; } catch (ArithmeticException e) {     System.out.println("Cannot divide by zero!"); } finally {     System.out.println("This will always be printed."); } 

22. 文件I/O

读取文件

import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException;  String line; try (BufferedReader br = new BufferedReader(new FileReader("file.txt"))) {     while ((line = br.readLine()) != null) {         System.out.println(line);     } } catch (IOException e) {     e.printStackTrace(); } 

写入文件

import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException;  try (BufferedWriter bw = new BufferedWriter(new FileWriter("output.txt"))) {     bw.write("Hello World!"); } catch (IOException e) {     e.printStackTrace(); } 

23. 多线程

创建线程

class MyThread extends Thread {     public void run() {         System.out.println("MyThread running");     } }  MyThread myThread = new MyThread(); myThread.start(); 

实现Runnable接口

class MyRunnable implements Runnable {     public void run() {         System.out.println("MyRunnable running");     } }  Thread thread = new Thread(new MyRunnable()); thread.start(); 

24. 同步

public class Counter {     private int count = 0;      public synchronized void increment() {         count++;     }      public synchronized int getCount() {         return count;     } } 

25. 高级多线程

使用Executors

import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;  ExecutorService executor = Executors.newFixedThreadPool(2);  executor.submit(() -> {     System.out.println("ExecutorService running"); });  executor.shutdown(); 

Future和Callable

import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future;  Callable callableTask = () -> {     return 10; };  ExecutorService executorService = Executors.newSingleThreadExecutor(); Future future = executorService.submit(callableTask);  try {     Integer result = future.get(); // this will wait for the task to finish     System.out.println("Future result: " + result); } catch (InterruptedException | ExecutionException e) {     e.printStackTrace(); } finally {     executorService.shutdown(); } 

以上就是Java常见的50个代码示例，涵盖了从基础到高级的多方面知识。掌握这些代码片段将极大提升你的编码技能，并为成长为一名优秀的Java架构师打下坚实基础。持续实践和学习，相信不久的将来，你将在Java的世界里驾轻就熟。