50个JAVA常见代码大全：学完这篇从Java小白到架构师

古城微笑少年丶 2024-02-05 21:41 17阅读 0赞

## 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。