50个JAVA常见代码大全：学完这篇从Java小白到架构师

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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<T> { 
    private T t; public void set(T t) { 
    this.t = t; } public T get() { 
    return t; } } Box<Integer> 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<String> 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<String, Integer> 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<Integer> callableTask = () -> { 
    return 10; }; ExecutorService executorService = Executors.newSingleThreadExecutor(); Future<Integer> 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。