java Math.ceil int向上取整 不对 正确用法

import java.io.*;
class test  
{
	public static void main (String[] args) throws java.lang.Exception
	{
		System.out.println("hi");
		int a = (int) Math.ceil(100/40);
		System.out.println(a);
		
		double b = Math.ceil(100/40);
		System.out.println(b);
		
		int c = (int) Math.ceil((double)100/40);
		System.out.println(c);
		
		
	}
}