当前位置：首页 > article >正文

Java 快速入门指南

article 2025/9/13 23:27:09

Java 快速入门指南

1. 安装 Java

从 Oracle 官方网站下载并安装最新版本的 Java Development Kit (JDK)。
安装集成开发环境 (IDE)，如 IntelliJ IDEA、Eclipse 或 NetBeans。

2. 基本语法

2.1 变量和数据类型

Java 支持多种数据类型，如整数、浮点数、字符、字符串和布尔值。以下是一些示例代码：

public class Main {public static void main(String[] args) {// 数字int a = 10;double b = 3.14;// 字符char c = 'A';// 字符串String name = "Alice";// 布尔值boolean isActive = true;// 数组int[] numbers = {1, 2, 3, 4, 5};System.out.println("Name: " + name);}
}

2.2 基本操作

public class Main {public static void main(String[] args) {int a = 10;double b = 3.14;// 算术运算int sum = a + (int)b;int difference = a - (int)b;double product = a * b;double quotient = a / b;// 字符串操作String name = "Alice";String greeting = "Hello, " + name;// 数组操作int[] numbers = {1, 2, 3, 4, 5};numbers[0] = 10;System.out.println("Sum: " + sum);System.out.println(greeting);}
}

3. 控制结构

3.1 条件语句

Java 使用 if、else if 和 else 进行条件判断：

public class Main {public static void main(String[] args) {int a = 10;int b = 5;if (a > b) {System.out.println("a is greater than b");} else if (a == b) {System.out.println("a is equal to b");} else {System.out.println("a is less than b");}}
}

3.2 循环

Java 支持 for、while 和 do-while 循环：

public class Main {public static void main(String[] args) {// for 循环for (int i = 0; i < 5; i++) {System.out.println("i: " + i);}// while 循环int count = 0;while (count < 5) {System.out.println("count: " + count);count++;}// do-while 循环int num = 0;do {System.out.println("num: " + num);num++;} while (num < 5);}
}

4. 函数

函数用 return_type 和 function_name 定义：

public class Main {public static void main(String[] args) {int sum = add(10, 20);System.out.println("Sum: " + sum);}public static int add(int x, int y) {return x + y;}
}

5. 类和对象

Java 是面向对象的编程语言，可以定义类和创建对象：

public class Person {private String name;private int age;public Person(String name, int age) {this.name = name;this.age = age;}public void introduce() {System.out.println("My name is " + name + " and I am " + age + " years old.");}public static void main(String[] args) {Person alice = new Person("Alice", 25);alice.introduce();}
}

6. 继承和多态

Java 支持继承和多态，允许子类继承父类的方法和属性，并可以重写方法：

class Animal {public void makeSound() {System.out.println("Some sound...");}
}class Dog extends Animal {@Overridepublic void makeSound() {System.out.println("Woof");}
}public class Main {public static void main(String[] args) {Animal myDog = new Dog();myDog.makeSound();}
}

7. 接口和抽象类

接口和抽象类提供了更高的抽象层次，允许定义方法而不实现它们：

7.1 接口

interface Animal {void makeSound();
}class Dog implements Animal {public void makeSound() {System.out.println("Woof");}
}public class Main {public static void main(String[] args) {Animal myDog = new Dog();myDog.makeSound();}
}

7.2 抽象类

abstract class Animal {public abstract void makeSound();public void sleep() {System.out.println("Zzz");}
}class Dog extends Animal {public void makeSound() {System.out.println("Woof");}
}public class Main {public static void main(String[] args) {Dog myDog = new Dog();myDog.makeSound();myDog.sleep();}
}

8. 集合框架

Java 提供了丰富的集合框架，包括 ArrayList、HashMap 等：

import java.util.ArrayList;
import java.util.HashMap;public class Main {public static void main(String[] args) {// ArrayListArrayList<String> names = new ArrayList<>();names.add("Alice");names.add("Bob");System.out.println(names.get(0));// HashMapHashMap<String, Integer> ages = new HashMap<>();ages.put("Alice", 25);ages.put("Bob", 30);System.out.println(ages.get("Alice"));}
}

9. 异常处理

使用 try、catch 和 finally 处理异常：

public class Main {public static void main(String[] args) {try {int a = 10;int b = 0;int c = a / b;} catch (ArithmeticException e) {System.out.println("Error: " + e.getMessage());} finally {System.out.println("This will always execute.");}}
}

10. 文件操作

Java 提供了丰富的文件操作支持：

import java.io.*;public class Main {public static void main(String[] args) {// 写入文件try (BufferedWriter writer = new BufferedWriter(new FileWriter("example.txt"))) {writer.write("Hello, world!");} catch (IOException e) {e.printStackTrace();}// 读取文件try (BufferedReader reader = new BufferedReader(new FileReader("example.txt"))) {String line;while ((line = reader.readLine()) != null) {System.out.println(line);}} catch (IOException e) {e.printStackTrace();}}
}