public class StringDemo{
public static void main(String[] args) {
String str = "this:";
int a = str.indexOf(":"); // returns 4
String subStr = str.substring(a+1); // returns "" <empty string>
String subStr = str.substring(a+2); // throws exception
int charAt = str.charAt(a+1); // Throws an StringIndexOutOfBoundsExp.
}
}
can any one explain why is it returning "" and why it throws an exception
str.substring(a+1)
returns the string after the given index (a+1), which is the string after the colon which is an empty string.
str.charAt(a+1)
accesses the array value at the position after the colon which doesn't exist.
str.substring(a+1) returns a substring from str STARTING at a+1 or 5. Your string doesn't have anything at index 5 so it will return an empty string.
.substring() will return a blank string when you call it with the size of the string, it will simply return a new empty string. Anything greater and it will throw an exception.No it won't throw IndexOutOfBoundException instead it will return empty String.
Same is the case when beginIndex and endIndex is equal, in case of second method. It will only throw StringIndexBoundException when beginIndex is negative, larger than endIndex or larger than length of String.
String subStr = str.substring(a+1); // returns "" . // Because there is Nothing at that place
Its clearly there in the API
"emptiness".substring(9) returns "" (an empty string)
Read more: http://javarevisited.blogspot.com/2011/10/how-substring-in-java-works.html#ixzz2SVu5lyYo
where as CharAt throws Throws:
IndexOutOfBoundsException - if the index argument is negative or not less than the length of this string
I would like to answer first why the result is empty string.
Method:substring(int beginIndex)
is like saying
substring(beginIndex,String.length());
the endIndex specified on your argument is 5 and the length is also 5. Thus if you do substring(0,0) or substring(1,1) or substring(5,5), it will always give an empty string because begin and end Index is equal. To put it in simple language, same begin and end index occupies nothing thus result to empty string.
Why the integer 5 is still a valid index? the answer lies on the Java API itself: Throws: IndexOutOfBoundsException - if beginIndex is negative or larger than the length of this String object.
Reference:
