gfanna.blogg.se - Java substring indexof

JAVA SUBSTRING INDEXOF CODE

The code could be simplified, but I've intentionally made it verbose so you can easily step through it in a debugger. For consistency with item 2, negative return values also start counting down starting with -1 as the index of the last character.

For that reason, we use -1 to refer to the index of the last character, and continue counting backwards from there.

Because we cannot test for int -0, we cannot refer to the index of the last character as -0.

Integer.MIN_VALUE is now returned if the search string is not found. But because -1 is a valid index in our new implementation, we need to define a new contract.

String.indexOf normally returns -1 if the search string is not found.

However, you can get close to what you want. We can pass the index of the character to start searching from. This method returns the index within this string of the first occurrence of the specified substring, starting at the specified index. implementing a generic indexOf which accepts a negative index and returns the appropriate negative index (if there is one) is more complicated because Java does not distinguish between int 0 and int -0 (both will be represented as 0), and because String.indexOf normally returns -1 if the search string is not found. The method indexOf() returns the first occurrence index of a character or a String in another String. Getting back to your second example: "abcd".indexOf("d",-0) Return (targetCount = 0 ? sourceCount : -1) The indexOf() method returns the index number where the target string is first found or -1 if the target is not found.

As it turns out, the indexOf implementation that is ultimately called resets a negative fromIndex value to zero: static int indexOf(char source, int sourceOffset, int sourceCount,Ĭhar target, int targetOffset, int targetCount, To answer your question about what happens when you pass a negative number, you can dig into the source code for the String class. This method may be used to trim whitespace (as defined above) from the beginning and end of a string. That's because indexOf (String) is a JVM intrinsic: its Java code is actually replaced by JIT compiler with efficient inline implementation. The indexOfString is slightly faster for direct access, but somewhat slower for indirect. You can also use lastIndexOf(int ch, int fromIndex)if you want to search backwards from a particular index. A String object is returned, representing the substring of this string that begins with the character at index k and ends with the character at index m -that is, the result of this.substring (k, m + 1). As you can see, indexOfChar performs in the same way regardless of direct or indirect access. Then you could subtract that number from the length of the String and negate it, if that's what you really want. LastIndexOf(int ch) will start from the end and search backwards, returning the absolute index of the last occurrence.