Parameters: beginIndex - the beginning index, inclusive. "hamburger".substring(4, 8) returns "urge" "emptiness".substring(9) returns "" (an empty string) The length of the substring is endIndex-beginIndex.Įxamples: "unhappy".substring(2) returns "happy" The substring begins at the specified beginIndexĪnd extends to the character at index endIndex - 1. Public String substring(int beginIndex, int endIndex) The substring begins with the "" characterĪt the specified index and extends to the end of this string. Returns a new string that is a substring of this
Redefining of course would mean rewriting the entire internet, so it's not likely.įrom String API javadoc: public String substring(int beginIndex) Or the method redefined to match C++ string::substr method. The Java method signature should be: public String substring(int beginIndex, The second parameter is not named correctly. This is just one of those times that you have to remember the idiosyncrasy of this method. If we rename parameter 2 to "lengthOfSubstringFromIndex0" you don't have to do the endIndex - 1 count, and it never throws the IndexOutOfBoundsException() that is expected when specifying an endIndex, 10, that is out of range for the underlying array. If we use 10 as the 'endIndex' parameter,ĪssertThat(testString.substring(4, 10), equalTo("String")) The length of testString from index 0 to char 'g' in 'String' is 10 chars. If we test the method in JUnit with concrete values looking at the C++ method, we expect:ĪssertThat(testString.substring(4, 6), equalTo("String")) īut of course we get Expected: "String" but was "St" Specifying an endIndex of 10 should always throw the IndexOutOfBoundsException() because testString has no endIndex of 10. TestString has 10 chars, index positions 0 to 9. Number of characters to include in the substring (if the string is shorter, as many characters as possible are used). Note that the second parameter in the method definition is 'len' for length. String substr (size_t pos = 0, size_t len = npos) const From C+++ string class we see the method definition is: We know that Gosling based the Java syntax on the C/C++ languages for familiarity. Length - the length of the string desired beginning at beginIndex. The most likely case is that the second parameter was misnamed. Java/C/C++ and every other language that I know of does NOT view the array index as the 'divider' between array elements.īeginIndex - the beginning index, inclusive.Įither endIndex is misnamed because the language does not allow memory access to the address at endIndex + 1 which is required to include the last array element OR endIndex is mis-defined and must be:
Java substring start and end index equals 0 software#
I view this as a software fault in the Java String.substring(int beginIndex, int endIndex) method. You will also get an error if the startIndex is larger than the endIndex.I know this thread is quite old but this is such a fundamental problem that I think it warrants clarification.
Note: If the startIndex or endIndex is negative or larger than the string's length, you will get an error. Working of Java String substring() method If the endIndex is not passed, the substring beings with the character at the specified index and extends to the end of the string.The substring beings with the character at the startIndex and extends to the character at index endIndex - 1.
The substring() method returns a substring from the given string. The substring() method takes two parameters. The syntax of the substring() method is: string.substring(int startIndex, int endIndex)
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