Java快速IO实现

📚 众所周知，Java的Scanner是真的慢，要是放在算法上基本数据还没读完就TLE了，再加上今年参加的是Java的蓝桥杯竞赛，数据读写上可不能掉链子，于是乎，就有了这篇实现Java快速读写的文章。

介绍

在使用之前我先介绍下StreamTokenizer green类：

• StreamTokenizer说快但是也并没有比Scanner快多少（反正没有scanf快是真的）
• 在使用时StreamTokenizer会为每个数据解析为Token，他的nextToken方法用于读取下一个标记。
• 它的nval字段用于获取具体的数据，返回类型是double所以要进行强转
• 每次使用nval读入数据之前必须要调用nextToken
• sval字段用于读取字符串

模板代码

import java.io.*;

/**
 * Created By XuanRan on 2021/12/3
 * 快速IO模板
 */
public class QuickIO {

    private static StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
    private static PrintStream out = System.out;

    public static void main(String[] args) throws IOException {
        String s = next();
        out.println(s);
        out.flush();
        out.close();
    }

    public static int nextInt() throws IOException {
        in.nextToken();
        return (int) in.nval;
    }

    public static String next() throws IOException {
        in.nextToken();
        return in.sval;
    }
}

举例

以洛谷中P1177快速排序题目为例子，使用快速读写和Arrays的sort方法就能轻松通过此题，但如果使用Scanner提供的方法会相对慢100ms-300ms左右，在OI中相差100ms可是不小的差距了。

• 快速读写方式

import java.io.*;
import java.util.Arrays;

/**
 * Created By XuanRan on 2021/12/3
 */
public class P1177快速排序 {

    static StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
    static PrintStream out = System.out;
    static StringBuilder builder = new StringBuilder();

    public static void main(String[] args) throws Exception {
        int N = nextInt();
        int[] arr = new int[N + 100];
        for (int i = 1; i <= N; i++) {
            arr[i] = nextInt();
        }
        Arrays.sort(arr, 1, N + 1);
        for (int i = 1; i <= N; i++) {
            builder.append(arr[i]).append(" ");
        }
        out.println(builder.toString());
    }

    private static int nextInt() throws Exception {
        in.nextToken();
        return (int) in.nval;
    }

    private static String next() throws Exception {
        in.nextToken();
        return in.sval;
    }
}

• 普通方式

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.io.StreamTokenizer;
import java.util.Arrays;
import java.util.Scanner;

/**
 * Created By XuanRan on 2021/12/3
 */
public class P1177快速排序2 {

    static StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
    static PrintStream out = System.out;
    static StringBuilder builder = new StringBuilder();

    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int[] arr = new int[N + 100];
        for (int i = 1; i <= N; i++) {
            arr[i] = scanner.nextInt();
        }
        Arrays.sort(arr, 1, N + 1);
        for (int i = 1; i <= N; i++) {
            System.out.print(arr[i] + " ");
        }

    }

    private static int nextInt() throws Exception {
        in.nextToken();
        return (int) in.nval;
    }

    private static String next() throws Exception {
        in.nextToken();
        return in.sval;
    }
}