Java program to extract coefficents from quadratic equation

Problem: Java program to split the coefficients from a quadratic equation eg if input string is:

String str1;
str1 = "4x2-4x-42=0"

So I need to split the coefficients from the given input string and to get output as

a = 4 b = -4 c = -42

I tried this:

String equation = "ax2+bx-c=0";
String[] parts = equation.split("\\+|-|=");
for (int i = 0; i < parts.length - 2; i++) {
    String part = parts[i].toLowerCase();
    System.out.println(part.substring(0, part.indexOf("x")));
}
System.out.println(parts[2]);

But I got the output as 23x2 and 4x and 4. Actual output needed is 23 ,- 4 , 4.