Java

BigDecimal和BigInteger的区别主要在于除法会除不尽，需要指定精确到小数点后多少位以及舍入方法。

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

public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Solver solver = new Solver();
		solver.solve(in, out);
		out.close();
	}

	static class Solver {
		public void solve(InputReader in, PrintWriter out) {
			BigDecimal d1=BigDecimal.valueOf(1);
			BigDecimal d2=BigDecimal.valueOf(7);
			
			out.print(d1+"/"+d2+"=");
			out.println(d1.divide(d2, 30, RoundingMode.HALF_UP));
		}

	}

	static class InputReader {
		public BufferedReader reader;
		public StringTokenizer tokenizer;

		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		}

		public String next() {
			while (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}
		
		public long nextLong() {
			return Long.parseLong(next());
		}

	}
	
}