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

<code>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。