geuni

charAt

public char charAt(int index)

Returns the character at the specified index. An index ranges from 0 to length() - 1. The first character of the sequence is at index 0, the next at index 1, and so on, as for array indexing.  

Parameters:

index - the index of the character.

Returns:

the character at the specified index of this string. The first character is at index 0.

Throws:

IndexOutOfBoundsException - if the index argument is negative or not less than the length of this string.

length

public int length()

Returns the length of this string. The length is equal to the number of 16-bit Unicode characters in the string.

Returns:

the length of the sequence of characters represented by this object.

indexOf

public int indexOf(String str)

Returns the index within this string of the first occurrence of the specified substring. The integer returned is the smallest value k such that:

this.startsWith(str, k)

is true.

Parameters:

str - any string.

Returns:

if the string argument occurs as a substring within this object, then the index of the first character of the first such substring is returned; if it does not occur as a substring, -1 is returned.

Throws:

NullPointerException - if str is null.

substring

public String substring(int beginIndex,int endIndex)

Returns a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.

Examples:

"hamburger".substring(4, 8) returns "urge"

"smiles".substring(1, 5) returns "mile"

Parameters:

beginIndex - the beginning index, inclusive.

endIndex - the ending index, exclusive.

Returns:

the specified substring.

Throws:

IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex.

concat

public String concat(String str)

Concatenates the specified string to the end of this string.

If the length of the argument string is 0, then this String object is returned. Otherwise, a new String object is created, representing a character sequence that is the concatenation of the character sequence represented by this String object and the character sequence represented by the argument string.

Examples:

"cares".concat("s") returns "caress"

"to".concat("get").concat("her") returns "together"

Parameters:

str - the String that is concatenated to the end of this String.

Returns:

a string that represents the concatenation of this object's characters followed by the string argument's characters.

Throws:

NullPointerException - if str is null.

replace

public String replace(char oldChar,char newChar)

Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.

If the character oldChar does not occur in the character sequence represented by this String object, then a reference to this String object is returned. Otherwise, a new String object is created that represents a character sequence identical to the character sequence represented by this String object, except that every occurrence of oldChar is replaced by an occurrence of newChar.

Examples:

"mesquite in your cellar".replace('e', 'o')

        returns "mosquito in your collar"

"the war of baronets".replace('r', 'y')

        returns "the way of bayonets"

"sparring with a purple porpoise".replace('p', 't')

        returns "starring with a turtle tortoise"

"JonL".replace('q', 'x') returns "JonL" (no change)

Parameters:

oldChar - the old character.

newChar - the new character.

Returns:

a string derived from this string by replacing every occurrence of oldChar with newChar.

toLowerCase

public String toLowerCase()

Converts all of the characters in this String to lower case using the rules of the default locale, which is returned by Locale.getDefault.

If no character in the string has a different lowercase version, based on calling the toLowerCase method defined by Character, then the original string is returned.

Otherwise, this method creates a new String object that represents a character sequence identical in length to the character sequence represented by this String object, with every character equal to the result of applying the method Character.toLowerCase to the corresponding character of this String object.

Examples:

"French Fries".toLowerCase() returns "french fries"

Returns:

the string, converted to lowercase.

See Also:

Character.toLowerCase(char), toUpperCase()

trim

public String trim()

Removes white space from both ends of this string.

If this String object represents an empty character sequence, or the first and last characters of character sequence represented by this String object both have codes greater than '\u0020' (the space character), then a reference to this String object is returned.

Otherwise, if there is no character with a code greater than '\u0020' in the string, then a new String object representing an empty string is created and returned.

Otherwise, let k be the index of the first character in the string whose code is greater than '\u0020', and let m be the index of the last character in the string whose code is greater than '\u0020'. A new String object is created, representing the substring of this string that begins with the character at index k and ends with the character at index m-that is, the result of this.substring(k, m+1).

This method may be used to trim whitespace from the beginning and end of a string; in fact, it trims all ASCII control characters as well.

Returns:

this string, with white space removed from the front and end.

public class StringTest {  

         public static void main(String[] args){

                   String free = "Freeman's Javajaby";

                   System.out.println(free.charAt(4));

                   System.out.println(free.length());

                   System.out.println(free.indexOf("e"));  

                   System.out.println(free.substring(3,12));

                   System.out.println(free.concat(" da")); 

                   System.out.println(free.replace('e', 't'));       

                   System.out.println(free.toLowerCase());

                   System.out.println(free.toUpperCase());

                   System.out.println(free.trim());

                   }                

}

결과 :  

m

18

2

eman's Ja

Freeman's Javajaby da

Frttman's Javajaby

freeman's javajaby

FREEMAN'S JAVAJABY

Freeman's Javajaby