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;```javadouble 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 {@Overridevoid 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 {@Overridevoid makeSound() {System.out.println("Bark");}
}public class Cat extends Animal {@Overridevoid 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 finishSystem.out.println("Future result: " + result);
} catch (InterruptedException | ExecutionException e) {e.printStackTrace();
} finally {executorService.shutdown();
}