Java 代码大全及详解需要涵盖 Java 语言的各个方面,包括基本语法、数据结构、面向对象编程、输入输出、网络编程等。
由于篇幅原因,我们无法在这里详细解释所有的 Java 代码,但是可以提供一些关键概念和示例代码。
以下是一些 Java 编程的基本概念和示例:
1、基本语法:
- Hello World 程序:
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
- 变量和数据类型:
int age = 30;
double salary = 5000.0;
char letter = 'A';
boolean isTrue = true;
String name = "John Doe";
- 条件语句:
if (age >= 18) {
System.out.println("You are an adult.");
} else {
System.out.println("You are not an adult.");
}
- 循环:
for (int i = 0; i < 10; i++) {
System.out.println("Iteration: " + i);
}
2、数据结构:
- 数组:
int[] numbers = {1, 2, 3, 4, 5};
- 列表:
import java.util.ArrayList;
import java.util.List;
List names = new ArrayList();
names.add("John");
names.add("Jane");
names.add("Doe");
- 集合:
import java.util.HashSet;
import java.util.Set;
Set uniqueNumbers = new HashSet();
uniqueNumbers.add(1);
uniqueNumbers.add(2);
uniqueNumbers.add(3);
- 映射:
import java.util.HashMap;
import java.util.Map;
Map nameAgeMap = new HashMap();
nameAgeMap.put("John", 30);
nameAgeMap.put("Jane", 28);
3、面向对象编程:
- 类和对象:
public class Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
}
Person person = new Person("John", 30);
继承和多态:
public class Employee extends Person {
private double salary;
public Employee(String name, int age, double salary) {
super(name, age);
this.salary = salary;
}
public double getSalary() {
return salary;
}
}
Person employee = new Employee("John", 30, 5000.0);
4、输入输出:
- 从控制台读取输入:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter your name: ");
String name = scanner.nextLine();
System.out.println("Hello, " + name + "!");
scanner.close();
}
}
- 文件读写:
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class Main {
public static void main(String[] args) {
try {
BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt"));
writer.write("Hello, World!");
writer.close();
BufferedReader reader = new BufferedReader(new FileReader("output.txt"));
String line = reader.readLine();
System.out.println(line);
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
5、网络编程:
- 简单的 HTTP 请求:
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
public class Main {
public static void main(String[] args) {
try {
URL url = new URL("https://api.example.com/data");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String line;
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
reader.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
以上仅为 Java 编程的一些基本概念和示例代码。
实际上,Java 语言及其生态系统包含了大量的类库、框架和设计模式,为开发者提供了强大的功能和灵活性。
要深入学习 Java 编程,建议参阅专业教材、在线教程和官方文档。