What is wrong with the following switch statement? 

// This code has errors!!!
switch (temp)
{
 case temp < 0 :
 System.out.println("Temp is negative.");
 break;
 case temp = 0:
 System.out.println("Temp is zero.");
 break;
 case temp > 0 :
 System.out.println("Temp is positive.");
 break;
}