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Java Strings

On this page:
• intro
• String
• find a word in a file
• StringTokenizer

 
Intro home - top of the page -

String objects can not be changed. But you can create a new object and point the same reference to this new object. There are MANY methods in the String class which can return a changed string, for example:
  String s1 = "mama went home";
  s1 = s1.replace('m', 'p');
  s1=s1.toUpperCase( );

If you have to make many changes in the string and you don't want to create a new immutable string object every time - use StringBuffer.

There are several methods allowing to search for characters or substring in a string, for example:
  int ii = s1.indexOf("WENT");

 
String home - top of the page -

public final class java.lang.String extends Object implements Comparable, Serializable

     String str = "abc";
     char data[] = {'a', 'b', 'c'};
     String str = new String(data);
     System.out.println("abc");
     String cde = "cde";
     System.out.println("abc" + cde);
     String c = "abc".substring(2,3);
     String d = cde.substring(1, 2);

String class defines only one Field:
static Comparator CASE_INSENSITIVE_ORDER
          Returns a Comparator that orders String objects as by compareToIgnoreCase.

Constructors:
String() - Initializes a newly created String object so that it represents an empty character sequence.
String(byte[] bytes) - Construct a new String by converting the specified array of bytes using the platform's default character encoding.
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 character-encoding name or that use the platform's default encoding.
String(byte[] bytes, int offset, int length) - Construct a new String by converting the specified subarray of bytes using the platform's default character encoding.
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 character-encoding name or that use the platform's default encoding.
String(byte[] bytes, int offset, int length, String enc) - Construct a new String by converting the specified subarray of bytes using the specified character encoding.
String(byte[] bytes, String enc) - Construct a new String by converting the specified array of bytes using the specified character encoding.

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(String value) - 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.

Methods (close to 50 of them):
char charAt(int index) - Returns the character at the specified index.

 int compareTo(Object o) - Compares this String to another Object.
 int compareTo(String anotherString) - Compares two strings lexicographically.
 int compareToIgnoreCase(String str) - Compares two strings lexicographically, ignoring case considerations.

 String concat(String str) - Concatenates the specified string to the end of this string.

static String copyValueOf(char[] data) - Returns a String that is equivalent to the specified character array.
static String copyValueOf(char[] data, int offset, int count) - Returns a String that is equivalent to the specified character array.

 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.

 byte[] getBytes() - Convert this String into bytes according to the platform's default character encoding, 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(String enc) method, which takes a character-encoding name, or the getBytes() method, which uses the platform's default encoding.
 byte[] getBytes(String enc) - Convert this String into bytes according to the specified character encoding, 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 hashcode 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.

 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 rightmost 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.
 int length() - Returns the length of this string.

 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.

 boolean startsWith(String prefix) - Tests if this string starts with the specified prefix.
 boolean startsWith(String prefix, int toffset) - Tests if this string starts with the specified prefix beginning a specified index.

 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, which is returned by Locale.getDefault.
 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, which is returned by Locale.getDefault.
 String toUpperCase(Locale locale) - Converts all of the characters in this String to upper case using the rules of the given locale.

 String trim() - Removes white space from both ends of this string.

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.

Methods inherited from class java.lang.Object:
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

 
Find a word in a file home - top of the page -

Here is a utility finding a word in a text file (case-insensitive) - and printing the line numbers and the lines with this word
 
/** 
  find a word in a text file
*/ 

import java.io.*; 

public class Grep { 
  static int line_num = 1;
  static String word;
  static String upper_word;
  static String line;

  public static void main(String [] args) { 

    if (args.length != 2) { 
      System.out.println("usage java Grep <word> <file>"); 
      System.out.println("Exiting."); 
      System.exit(0); 
    } 

    word = args[0];
    upper_word = word.toUpperCase();

    try { 
      BufferedReader in = new BufferedReader(new FileReader(args[1])); 

      while ((line = in.readLine()) != null) { 
        process_line(line);
        line_num++;
      }

      in.close(); 
    } 
    catch (IOException e) {System.err.println("Error: " + e);} 

  } // end main 

  static void process_line(String line){
     if ( (line.toUpperCase()).indexOf(upper_word)>=0) {
       System.out.println(line_num + ": " + line); 
     }
  }

} 

 
StringTokenizer home - top of the page -

public class StringTokenizer
extends Object
implements Enumeration
This code: 

         StringTokenizer st = new StringTokenizer("this is a test");
          while (st.hasMoreTokens()) {
              println(st.nextToken());
          }

prints the following output: 

          this
          is
          a
          test

StringTokenizer allows to break a string into tokens (see also more complex StreamTokenizer class).
The StringTokenizer methods do not distinguish among identifiers, numbers, and quoted strings, nor do they recognize and skip comments.
The set of delimiters (the characters that separate tokens) may be specified either at creation time or on a per-token basis.

If the returnDelims flag is false, delimiter characters serve to separate tokens.
If the returnDelims flag is true, delimiter characters are themselves considered to be tokens too.  A token is thus either one delimiter character, or a maximal sequence of consecutive characters that are not delimiters.

A StringTokenizer object internally maintains a current position within the string to be tokenized. Some operations advance this current position past the characters processed.

Constructors:
 StringTokenizer(String str) - Constructs a string tokenizer for the specified string.
 StringTokenizer(String str, String delim) - Constructs a string tokenizer for the specified string.
 StringTokenizer(String str, String delim, boolean returnDelims) - Constructs a string tokenizer for the specified string.

Methods:
int countTokens() - Calculates the number of times that this tokenizer's nextToken method can be called before it generates an exception.
boolean hasMoreElements() - Returns the same value as the hasMoreTokens method.
boolean hasMoreTokens() - Tests if there are more tokens available from this tokenizer's string.
Object nextElement() - Returns the same value as the nextToken method, except that its declared return value is Object rather than String.
String nextToken() - Returns the next token from this string tokenizer.
String nextToken(String delim) - Returns the next token in this string tokenizer's string.
 
Methods inherited from class java.lang.Object:
 clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 
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