자바 문자열 클레스 String

 

 

 

 

안녕하세요 오늘은 자바에 문자열 클레스인 String 에 대해서 알아보겠습니다.

 

 

막상 프로그래밍을 시작하면 자주 사용하는 클레스중 하나인 String 은

 

char 를 배열로 표현한 배열이라고 생각하시면 쉽습니다.

 

 

 

모든 클래스는  속성 +메소드 로 이루어저 있습니다.

 

 

일단 String 이 가지는 속성은  없다고 보시면 됩니다.

 

 

생성자

Constructor and Description
String() Initializes a newly created String object so that it represents an empty character sequence.
String(byte[] bytes) Constructs a new String by decoding the specified array of bytes using the platform's default charset.
String(byte[] bytes, Charset charset) Constructs a new String by decoding the specified array of bytes using the specified charset.
String(byte[] ascii, int hibyte) Deprecated.  This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a Charset, charset name, or that use the platform's default charset.
String(byte[] bytes, int offset, int length) Constructs a new String by decoding the specified subarray of bytes using the platform's default charset.
String(byte[] bytes, int offset, int length, Charset charset) Constructs a new String by decoding the specified subarray of bytes using the specified charset.
String(byte[] ascii, int hibyte, int offset, int count) Deprecated.  This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a Charset, charset name, or that use the platform's default charset.
String(byte[] bytes, int offset, int length, String charsetName) Constructs a new String by decoding the specified subarray of bytes using the specified charset.
String(byte[] bytes, String charsetName) Constructs a new String by decoding the specified array of bytes using the specified charset.
String(char[] value) Allocates a new String so that it represents the sequence of characters currently contained in the character array argument.
String(char[] value, int offset, int count) Allocates a new String that contains characters from a subarray of the character array argument.
String(int[] codePoints, int offset, int count) Allocates a new String that contains characters from a subarray of the Unicode code point array argument.
String(String original) Initializes a newly created String object so that it represents the same sequence of characters as the argument; in other words, the newly created string is a copy of the argument string.
String(StringBuffer buffer) Allocates a new string that contains the sequence of characters currently contained in the string buffer argument.
String(StringBuilder builder) Allocates a new string that contains the sequence of characters currently contained in the string builder argument.

 

 

메서드

 

Modifier and Type	Method and Description
char	charAt(int index) Returns the char value at the specified index.
int	codePointAt(int index) Returns the character (Unicode code point) at the specified index.
int	codePointBefore(int index) Returns the character (Unicode code point) before the specified index.
int	codePointCount(int beginIndex, int endIndex) Returns the number of Unicode code points in the specified text range of this String.
int	compareTo(String anotherString) Compares two strings lexicographically.
int	compareToIgnoreCase(String str) Compares two strings lexicographically, ignoring case differences.
String	concat(String str) Concatenates the specified string to the end of this string.
boolean	contains(CharSequence s) Returns true if and only if this string contains the specified sequence of char values.
boolean	contentEquals(CharSequence cs) Compares this string to the specified CharSequence.
boolean	contentEquals(StringBuffer sb) Compares this string to the specified StringBuffer.
static String	copyValueOf(char[] data) Returns a String that represents the character sequence in the array specified.
static String	copyValueOf(char[] data, int offset, int count) Returns a String that represents the character sequence in the array specified.
boolean	endsWith(String suffix) Tests if this string ends with the specified suffix.
boolean	equals(Object anObject) Compares this string to the specified object.
boolean	equalsIgnoreCase(String anotherString) Compares this String to another String, ignoring case considerations.
static String	format(Locale l, String format, Object... args) Returns a formatted string using the specified locale, format string, and arguments.
static String	format(String format, Object... args) Returns a formatted string using the specified format string and arguments.
byte[]	getBytes() Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
byte[]	getBytes(Charset charset) Encodes this String into a sequence of bytes using the given charset, storing the result into a new byte array.
void	getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin) Deprecated.  This method does not properly convert characters into bytes. As of JDK 1.1, the preferred way to do this is via the getBytes() method, which uses the platform's default charset.
byte[]	getBytes(String charsetName) Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
void	getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) Copies characters from this string into the destination character array.
int	hashCode() Returns a hash code for this string.
int	indexOf(int ch) Returns the index within this string of the first occurrence of the specified character.
int	indexOf(int ch, int fromIndex) Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
int	indexOf(String str) Returns the index within this string of the first occurrence of the specified substring.
int	indexOf(String str, int fromIndex) Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
String	intern() Returns a canonical representation for the string object.
boolean	isEmpty() Returns true if, and only if, length() is 0.
int	lastIndexOf(int ch) Returns the index within this string of the last occurrence of the specified character.
int	lastIndexOf(int ch, int fromIndex) Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
int	lastIndexOf(String str) Returns the index within this string of the last occurrence of the specified substring.
int	lastIndexOf(String str, int fromIndex) Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.
int	length() Returns the length of this string.
boolean	matches(String regex) Tells whether or not this string matches the given regular expression.
int	offsetByCodePoints(int index, int codePointOffset) Returns the index within this String that is offset from the given index by codePointOffset code points.
boolean	regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len) Tests if two string regions are equal.
boolean	regionMatches(int toffset, String other, int ooffset, int len) Tests if two string regions are equal.
String	replace(char oldChar, char newChar) Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
String	replace(CharSequence target, CharSequence replacement) Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.
String	replaceAll(String regex, String replacement) Replaces each substring of this string that matches the given regular expression with the given replacement.
String	replaceFirst(String regex, String replacement) Replaces the first substring of this string that matches the given regular expression with the given replacement.
String[]	split(String regex) Splits this string around matches of the given regular expression.
String[]	split(String regex, int limit) Splits this string around matches of the given regular expression.
boolean	startsWith(String prefix) Tests if this string starts with the specified prefix.
boolean	startsWith(String prefix, int toffset) Tests if the substring of this string beginning at the specified index starts with the specified prefix.
CharSequence	subSequence(int beginIndex, int endIndex) Returns a new character sequence that is a subsequence of this sequence.
String	substring(int beginIndex) Returns a new string that is a substring of this string.
String	substring(int beginIndex, int endIndex) Returns a new string that is a substring of this string.
char[]	toCharArray() Converts this string to a new character array.
String	toLowerCase() Converts all of the characters in this String to lower case using the rules of the default locale.
String	toLowerCase(Locale locale) Converts all of the characters in this String to lower case using the rules of the given Locale.
String	toString() This object (which is already a string!) is itself returned.
String	toUpperCase() Converts all of the characters in this String to upper case using the rules of the default locale.
String	toUpperCase(Locale locale) Converts all of the characters in this String to upper case using the rules of the given Locale.
String	trim() Returns a copy of the string, with leading and trailing whitespace omitted.
static String	valueOf(boolean b) Returns the string representation of the boolean argument.
static String	valueOf(char c) Returns the string representation of the char argument.
static String	valueOf(char[] data) Returns the string representation of the char array argument.
static String	valueOf(char[] data, int offset, int count) Returns the string representation of a specific subarray of the char array argument.
static String	valueOf(double d) Returns the string representation of the double argument.
static String	valueOf(float f) Returns the string representation of the float argument.
static String	valueOf(int i) Returns the string representation of the int argument.
static String	valueOf(long l) Returns the string representation of the long argument.
static String	valueOf(Object obj) Returns the string representation of the Object argument.

 

그러면 위의 내용을 가지고 일반적으로 자주 사용되는 예시를 보여드리겠습니다.

 

 ch배열과 String의 비교

 

public class StringExample{ 
public static void main(String args[]){ 

String s1="java";//creating string by java string literal 
char ch[]={'s','t','r','i','n','g','s'}; 
String s2=new String(ch);//converting char array to string 
String s3=new String("example");//creating java string by new keyword 
System.out.println(s1); 
System.out.println(s2); 
System.out.println(s3); 
}

} 

 

문자열 연결 메서드

 

class Testimmutablestring1{ 
 public static void main(String args[]){ 
   String s="Sachin"; 
   s=s.concat(" Tendulkar"); 
   System.out.println(s); 
  } 
} 

 

 

문자열 값 비교 equals  사용법

 

class Teststringcomparison1{ 
 public static void main(String args[]){ 
   String s1="Sachin"; 
   String s2="Sachin"; 
   String s3=new String("Sachin"); 
   String s4="Saurav"; 
   System.out.println(s1.equals(s2));//true 
   System.out.println(s1.equals(s3));//true 
   System.out.println(s1.equals(s4));//false 
 } 
} 

 

 문자열 주소 값 비교

 class Teststringcomparison3{ 
 public static void main(String args[]){ 
   String s1="Sachin"; 
   String s2="Sachin"; 
   String s3=new String("Sachin"); 
   System.out.println(s1==s2);//true (because both refer to same instance) 
   System.out.println(s1==s3);//false(because s3 refers to instance created in nonpool) 
 } 
} 

 

Substring 사용법

 

public class TestSubstring{ 
 public static void main(String args[]){ 
   String s="SachinTendulkar"; 
   System.out.println(s.substring(6));//Tendulkar 
   System.out.println(s.substring(0,6));//Sachin 
 } 
} 

 

 

public class LastTest{

public static void main(String args[]){

 

String s="Sachin"; 
System.out.println(s.toUpperCase());//SACHIN 
System.out.println(s.toLowerCase());//sachin 
System.out.println(s);//Sachin(no change in original) 

String s="  Sachin  "; 
System.out.println(s);//  Sachin   
System.out.println(s.trim());//Sachin 

String s="Sachin"; 
 System.out.println(s.startsWith("Sa"));//true 
 System.out.println(s.endsWith("n"));//true 

String s="Sachin"; 
System.out.println(s.charAt(0));//S 
System.out.println(s.charAt(3));//h 

String s="Sachin"; 
System.out.println(s.length());//6 

String s=new String("Sachin"); 
String s2=s.intern(); 
System.out.println(s2);//Sachin 

int a=10; 
String s=String.valueOf(a); 
System.out.println(s+10); 

 

String s1="Java is a programming language. Java is a platform. Java is an Island.";   
String replaceString=s1.replace("Java","Kava");//replaces all occurrences of "Java" to "Kava"   
System.out.println(replaceString); 

 

 

}

 

}

 

 

 

이상으로  String 클래스를 마치겠습니다 . 다음에는 유사 클레스인 StringBuffer로 돌아오겠습니다.