Java Exception throw creates an infinite loop - exception

Question

I have established a do-while loop to verify user input is valid. If a 0 or negative number is entered, the Exception is thrown and the catch prints out. However, if a string is entered (i.e., twenty instead of 20) it becomes an infinite loop constantly printing out "Invalid input!!", asking for user input, and printing out "Invalid input!!" again. Here's my code:
import java.util.Scanner;
public class Paint {
public static void main(String[] args) {
// Create object for the scanner class
Scanner scnr = new Scanner(System.in);
//Declare variables
double wallHeight = 0.0;
double wallWidth = 0.0;
double wallArea = 0.0;
double gallonsPaintNeeded = 0.0;
final double squareFeetPerGallons = 350.0;
//Implement a do-while loop to verify user provides valid input
do {
try {
//Prompt user for wall's height in feet
System.out.println("Enter wall height (feet): ");
wallHeight = scnr.nextDouble();
//Verify wallHeight is not less than or equal to zero
//If so, throw an exception
if(wallHeight <= 0) {
throw new Exception();
}
}
catch(Exception e) {
//Print invalid message
System.out.println("Invalid input!!");
}
}
while(wallHeight <= 0);
//Implement a do-while loop to verify user provides valid input
do {
try {
//Prompt user for wall's width in feet
System.out.println("Enter wall width (feet):");
wallWidth = scnr.nextDouble();
//Verify wallWidth is not less than or equal to zero
//If so, throw an exception
if(wallWidth <= 0) {
throw new Exception();
}
}
catch(Exception e) {
//Print invalid message
System.out.println("Invalid input");
}
}
while(wallWidth <= 0);
//Calculate wallArea
wallArea = wallHeight * wallWidth;
//Print wallArea
System.out.println("Wall area: " + wallArea + " square feet");
//Calculate gallonsPaintNeeded
gallonsPaintNeeded = wallArea / squareFeetPerGallons;
//Print paint needed
System.out.println("Paint needed: " + gallonsPaintNeeded + " gallons");
}
}