java如何读取输入

读取控制台输入

Java中读取控制台输入可以通过Scanner类或BufferedReader类实现。Scanner类更简单易用，适合基础输入需求；BufferedReader性能更高，适合处理大量输入。

使用Scanner类

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入内容: ");
        String input = scanner.nextLine();
        System.out.println("输入的内容是: " + input);
        scanner.close();
    }
}

使用BufferedReader类

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        System.out.print("请输入内容: ");
        String input = reader.readLine();
        System.out.println("输入的内容是: " + input);
    }
}

读取文件输入

读取文件内容可以使用Scanner、BufferedReader或Files类。Files类在Java 7及以上版本提供，适合快速读取小文件。

使用Scanner读取文件

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        try {
            Scanner scanner = new Scanner(new File("input.txt"));
            while (scanner.hasNextLine()) {
                String line = scanner.nextLine();
                System.out.println(line);
            }
            scanner.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}

使用BufferedReader读取文件

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        try (BufferedReader reader = new BufferedReader(new FileReader("input.txt"))) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

使用Files类读取文件

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        try {
            List<String> lines = Files.readAllLines(Paths.get("input.txt"));
            for (String line : lines) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

读取数字输入

处理数字输入时需要注意输入验证，避免非数字输入导致异常。

读取整数

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入一个整数: ");
        while (!scanner.hasNextInt()) {
            System.out.println("输入无效，请重新输入整数!");
            scanner.next();
        }
        int num = scanner.nextInt();
        System.out.println("输入的整数是: " + num);
        scanner.close();
    }
}

读取浮点数

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入一个浮点数: ");
        while (!scanner.hasNextDouble()) {
            System.out.println("输入无效，请重新输入浮点数!");
            scanner.next();
        }
        double num = scanner.nextDouble();
        System.out.println("输入的浮点数是: " + num);
        scanner.close();
    }
}

读取多行输入

处理多行输入时通常需要设置终止条件，例如空行或特定标记。

读取直到空行

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入多行内容，空行结束:");
        StringBuilder sb = new StringBuilder();
        String line;
        while (!(line = scanner.nextLine()).isEmpty()) {
            sb.append(line).append("\n");
        }
        System.out.println("输入的内容是:\n" + sb.toString());
        scanner.close();
    }
}

读取特定标记结束

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入多行内容，输入END结束:");
        StringBuilder sb = new StringBuilder();
        String line;
        while (!(line = scanner.nextLine()).equals("END")) {
            sb.append(line).append("\n");
        }
        System.out.println("输入的内容是:\n" + sb.toString());
        scanner.close();
    }
}