class String

Here is an excerpt of the documentation for class String. (Just because a method is listed here does not necessarily mean the method is or should be used on the exam.)

char charAt(int index)
Returns the char value at the specified index.
int compareTo( String anotherString )
Compares two strings lexicographically (alphabetically). The result is a negative integer if this String object lexicographically precedes the argument string. The result is a positive integer if this String object lexicographically follows the argument string. The result is zero if the strings are equal; compareTo returns 0 exactly when the equals(Object) method would return true.
String concat( String str )
Concatenates the specified string to the end of this string.
boolean equals( Object anObject )
Compares this string to the specified object.
int length()
Returns the length of this string.
String replace(String target, String replacement)
Returns a new string resulting from replacing all occurrences of target in this string with replacement.
String[] split( char separator )
Splits this string at each occurrence of separator. (None of the returned strings will contain separator.)
boolean startsWith(String prefix)
Tests whether this string starts with the specified prefix.
String substring(int beginIndex, int endIndex)
Return a new string which is a substring of this string. The substring begins at the specified beginIndex and extends the the character at index endIndex-1. Thus the length of the substring is endIndex-beginIndex. Note that the first character in the string is at index 0 (not index 1).

Examples:
"hamburger".substring(4,8) returns "urge"
"smiles".substring(1,5) returns "mile"
String toUpperCase()
Returns a copy of this string, with all of the characters converted to upper case.
String trim()
Returns a copy of the string, with leading and trailing spaces omitted.
static String valueOf(double d)
Returns the string representation of the double argument.