Program converting a given number from decimal to binary

DectoBin

/* package whatever; // don't place package name! */

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

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		BufferedReader reader=new BufferedReader(new InputStreamReader(System.in));
		BufferedWriter writer=new BufferedWriter(new OutputStreamWriter(System.out));
		int t=Integer.parseInt(reader.readLine()); //test cases
		while(t-->0)
		{
			int num=Integer.parseInt(reader.readLine());
			String res=""; // not efficient, look into StringBuffer
			while(num>0)
			{
				res+=(num%2)+"";
				num=num/2;
			}
			writer.write(printReverse(res)+"\n");
		}
	    writer.close();
	}
	
	static String printReverse(String s) //made static so that no object is required for a call
	{
		StringBuffer sb=new  StringBuffer(s);
		return sb.reverse().toString();
	}
}