Why doesn't following java code throw java.lang.StringIndexOutOfBoundsException when there is no element present at index 1?

Question

String str=\"x\";
System.out.println(str.substring(1));

From Javadoc:

String java.lang.String.substring(int beginIndex)

Answer 1

Take a look at the JavaDoc, and pay specific attention to the "emptiness" example:

Returns a string that is a substring of this string. The substring begins
with the character at the specified index and extends to the end of
this string. 

Examples: 

 "unhappy".substring(2) returns "happy"
 "Harbison".substring(3) returns "bison"
 "emptiness".substring(9) returns "" (an empty string)

Parameters:
beginIndex the beginning index, inclusive.
Returns:
the specified substring.
Throws:
IndexOutOfBoundsException - if beginIndex is negative or larger than
                            the length of this String object

An exception is throw if beginIndex is negative or larger than the length of this String object; in your case, beginIndex is equal to the length of your string, and not larger.