方法一：double 转 int

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

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter pw = new PrintWriter(System.out);

        double num = Double.parseDouble(br.readLine());
        pw.println((int) (num + 0.5));

        pw.flush();
        pw.close();
        br.close();
    }
}

方法二：字符串判断

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

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter pw = new PrintWriter(System.out);

        String str = br.readLine();
        int index = str.indexOf('.');
        String substr = str.substring(0, index);
        if (str.charAt(index + 1) < '5') {
            pw.println(substr);
        } else {
            pw.println(Integer.parseInt(substr) + 1);
        }

        pw.flush();
        pw.close();
        br.close();
    }
}