Question

Greetings,

Let’s say you wanted to test a string to see if it’s an exact match, or, if it’s a match with an _ and any number of characters appended following the _

Valid match examples:

MyTestString
MyTestString_
MyTestString_1234

If performance was a huge concern, which methods would you investigate? Currently I am doing the following:

if (String.equals(stringToMatch)) {
            // success
        } else {
            if (stringToMatch.contains(stringToMatch + "_")) {
                // success
            }
            // fail
        }

I tried replacing the pattern the String.contains _ with a Java.util.regex.Pattern match on _*, but that performed much worse. Is my solution here ideal or can you think of something more cleaver to improve performance a bit more?

Thanks for any thoughts

Answer 1

You can do something like

if(string.startsWith(testString)) {
    int len = testString.length();
    if(string.length() == len || string.charAt(len) == '_')
          // success
}

I assume you want the testString to appear even if you have a “_”?

---

EDIT: On whether to use one long condition or nested if statements, there is no difference in code or performance.

public static void nestedIf(boolean a, boolean b) {
    if (a) {
        if (b) {
            System.out.println("a && b");
        }
    }
}

public static void logicalConditionIf(boolean a, boolean b) {
    if (a && b) {
        System.out.println("a && b");
    }
}

compiles to the same code. If you do javap -c

public static void nestedIf(boolean, boolean);
  Code:
   0:   iload_0
   1:   ifeq    16
   4:   iload_1
   5:   ifeq    16
   8:   getstatic       #7; //Field java/lang/System.out:Ljava/io/PrintStream;
   11:  ldc     #8; //String a && b
   13:  invokevirtual   #9; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   16:  return

public static void logicalConditionIf(boolean, boolean);
  Code:
   0:   iload_0
   1:   ifeq    16
   4:   iload_1
   5:   ifeq    16
   8:   getstatic       #7; //Field java/lang/System.out:Ljava/io/PrintStream;
   11:  ldc     #8; //String a && b
   13:  invokevirtual   #9; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   16:  return

The complied code is identical.