IB Computer Science Strings and Characters in Java

Just google “Java String Class”, to see all the methods that can be used with a String object.

Length Methods

The method int length () returns the number of characters in a the calling String s1

len = s1.length()

Comparison Methods

You have learned how to test if two strings are equal to each other using the boolean equals (String s) method, which takes into account the case of the characters in the two strings. Returns a true or false value.

s1.equals (s2)

The method boolean equalsIgnoreCase (String s) compares equality between two strings without taking into the case of the characters in the two strings. Returns a true or false value.

s1.equalsIgnoreCase (s2)

The method boolean compareTo (String s) compares strings alphabetically taking into consideration the case of the characters in the two strings.

s1.compareTo (s2)

The method boolean compareToIgnoreCase (String s) compares strings alphabetically taking into consideration the case of the characters in the two strings

s1.compareToIgnoreCase (s2)

Both compareTo and compareToIgnoreCase return an integer value
▪ returns a 0 if the two strings are alphabetically equal
▪ returns a negative number if s1 is alphabetically before s2
▪ returns a positive number if s1 is alphabetically after s2

The method boolean startsWith (String s) returns true if the calling string starts with the specified substring s

s1.startsWith (s)

The method boolean startsWith (String s, int offset) returns true if the calling string starts with the specified substring s starting from the index offset

s1.startsWith (s, #)

The method boolean endsWith (String s) returns true if the calling string ends with the specified substring s

s1.endsWith (s)

Conversion Methods

Sometimes it is useful for a string to be modified in some manner. You cannot change the original string object with any of the methods outlined below, but they will create a new string or array that you can use to overwrite the original if need be.

The method String copyValueOf (char data ) returns a new String the represents the characters in the character array data.
String s1 = String.copyValueOf (charArray );

The method String copyValueOf (char data, int start, int stop) returns a new String the represents the characters in the character array data starting at position start and ending at position stop

s1 = String.copyValueOf (charArray );

The method String toLowerCase ( ) returns a new String with all the characters of the original string in lower case. The original string is not altered.

s2 = s1.toLowerCase ( );

The method String toUpperCase ( ) returns a new String with all the character of the original string in upper case. The original string is not altered.
s2 = s1.toUpperCase ( );

The method String replace (char oldChar, char newChar) returns a new string resulting from replacing all occurrences of oldChar in the original string with newChar. The original string is not altered

s2 = s1.replace(old,new);

The method String replaceAll (String s, String r) returns a new string resulting from replacing all occurrences of the substring s in the original string with the substring r. The original string is not altered

s2 = s1.replaceAll (s,r);

The method String replaceFirst(String s, String r) returns a new string resulting from replacing the first occurrence of the substring s in the original string with the substring r. The original string is not altered

s2 = s1.replaceFirst (s,r);