Does java have a built-in method to compare precedence of two operators? For example, if I have a char '/' and a char '+' is there a method I can call that compares the two and returns true/false if the first is greater than the second (e.g. true)?
4 Answers
Operator precedence the way you defined it, while common, is not a universal truth that the Java language should recognize. Therefore no, Java language itself does not have such comparison. It is of course easy to write your own:
int precedenceLevel(char op) {
switch (op) {
case '+':
case '-':
return 0;
case '*':
case '/':
return 1;
case '^':
return 2;
default:
throw new IllegalArgumentException("Operator unknown: " + op);
}
}
Then given char op1, op2, just compare precedenceLevel(op1), precedenceLevel(op2).
You can also use if-else, or ternary operators instead of switch if you only have very few operators. Another option would be to use an enum Operator implements Comparable<Operator>, but depending on what you're doing, perhaps a parsing tool like ANTLR is the better.
Note that the above example puts ^ at the highest precedence, implying that perhaps it's used to denote exponentiation. In fact, ^ in Java language is the exclusive-or, and it has a lower precedence than +.
System.out.println(1+2^3); // prints 0
System.out.println(1+(2^3)); // prints 2
System.out.println((1+2)^3); // prints 0
This just goes to show that the precedence and even semantics of these symbols are NOT universal truths.
See also:
Comments
I am puzzled why you think you need this information at run-time. In every language I have ever used including algebra and English, operator precedence is predefined.