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Java String类

Java String类使用代码实例 -字符串String，被广泛使用在Java编程中，一个字符序列。在Java编程语言中，字符串是对象。

字符串，被广泛使用在Java编程中，一个字符序列。在Java编程语言中，字符串是对象。

Java平台提供了创建和操作字符串String类。

创建String:

最直接的方法来创建一个字符串是这样写： 

String greeting = "Hello world!";

每当遇到一个字符串文字在你的代码中，编译器会创建一个String对象，它的值在本例中，“你好，世界！”。
任何其他对象，可以创建String对象使用new关键字和构造。 String类有11构造函数，可以提供不同的来源，如一个字符数组，字符串使用的初始值： 

public class StringDemo{
   public static void main(String args[]){
      char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.'};
      String helloString = new String(helloArray);  
      System.out.println( helloString );
   }
}

这将产生以下结果： 

hello

Note: The String class is immutable, so that once it is created a String object cannot be changed. If there is a necessity to make alot of modifications to Strings of characters then you should use String Buffer & String Builder Classes.

String长度:

被称为访问器方法使用的方法，以获得有关对象的信息。一个访问方法，可以使用字符串的 length() 方法，该方法返回String对象中包含的字符数。
在下面的两行代码被执行了，长度等于17： 

public class StringDemo{
   public static void main(String args[]){
      String palindrome = "Dot saw I was Tod";
      int len = palindrome.length();
      System.out.println( "String Length is : " + len );
   }
}

这将产生以下结果： 

String Length is : 17

连接字符串String：

String类包括连接两个字符串的方法： 

string1.concat(string2);

This returns a new string that is string1 with string2 added to it at the end. You can also use the concat() method with string literals, as in: 

"My name is ".concat("Zara");

Strings are more commonly concatenated with the + operator, as in: 

"Hello," + " world" + "!"

which results in: 

"Hello, world!"

Let us look at the followinge example: 

public class StringDemo{
   public static void main(String args[]){
      String string1 = "saw I was ";
      System.out.println("Dot " + string1 + "Tod");
   }
}

This would produce following result: 

Dot saw I was Tod

创建格式字符串：

printf()和format()方法来打印输出格式的数字。 String类有一个等价类的方法，format()，该函数返回一个String对象，而不是一个PrintStream对象。

使用String的静态format()方法允许你创建一个格式化字符串，可以重复使用，而不是一次性打印语句。例如： 

System.out.printf("The value of the float variable is " +
                  "%f, while the value of the integer " +
                  "variable is %d, and the string " +
                  "is %s", floatVar, intVar, stringVar);

you can write: 

String fs;
fs = String.format("The value of the float variable is " +
                   "%f, while the value of the integer " +
                   "variable is %d, and the string " +
                   "is %s", floatVar, intVar, stringVar);
System.out.println(fs);

String方法:

下面是String类所支持的列表的方法：

SN Methods with Description
1 char charAt(int index) 
Returns the character at the specified index.
2 int compareTo(Object o) 
Compares this String to another Object.
3 int compareTo(String anotherString)
Compares two strings lexicographically.
4 int compareToIgnoreCase(String str) 
Compares two strings lexicographically, ignoring case differences.
5 String concat(String str)
Concatenates the specified string to the end of this string.
6 boolean contentEquals(StringBuffer sb) 
Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer.
7 static String copyValueOf(char[] data) 
Returns a String that represents the character sequence in the array specified.
8 static String copyValueOf(char[] data, int offset, int count)
Returns a String that represents the character sequence in the array specified.
9 boolean endsWith(String suffix) 
Tests if this string ends with the specified suffix.
10 boolean equals(Object anObject)
Compares this string to the specified object.
11 boolean equalsIgnoreCase(String anotherString)
Compares this String to another String, ignoring case considerations.
12 byte getBytes() 
Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
13 byte[] getBytes(String charsetName
Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
14 void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
Copies characters from this string into the destination character array.
15 int hashCode()
Returns a hash code for this string.
16 int indexOf(int ch) 
Returns the index within this string of the first occurrence of the specified character.
17 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.
18 int indexOf(String str)
Returns the index within this string of the first occurrence of the specified substring.
19 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.
20 String intern()
Returns a canonical representation for the string object.
21 int lastIndexOf(int ch) 
Returns the index within this string of the last occurrence of the specified character.
22 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.
23 int lastIndexOf(String str)
Returns the index within this string of the rightmost occurrence of the specified substring.
24 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.
25 int length() 
Returns the length of this string.
26 boolean matches(String regex)
Tells whether or not this string matches the given regular expression.
27 boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len) 
Tests if two string regions are equal.
28 boolean regionMatches(int toffset, String other, int ooffset, int len)
Tests if two string regions are equal.
29 String replace(char oldChar, char newChar)
Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
30 String replaceAll(String regex, String replacement
Replaces each substring of this string that matches the given regular expression with the given replacement.
31 String replaceFirst(String regex, String replacement) 
Replaces the first substring of this string that matches the given regular expression with the given replacement.
32 String[] split(String regex) 
Splits this string around matches of the given regular expression.
33 String[] split(String regex, int limit) 
Splits this string around matches of the given regular expression.
34 boolean startsWith(String prefix)
Tests if this string starts with the specified prefix.
35 boolean startsWith(String prefix, int toffset)
Tests if this string starts with the specified prefix beginning a specified index.
36 CharSequence subSequence(int beginIndex, int endIndex)
Returns a new character sequence that is a subsequence of this sequence.
37 String substring(int beginIndex)
Returns a new string that is a substring of this string.
38 String substring(int beginIndex, int endIndex)
Returns a new string that is a substring of this string.
39 char[] toCharArray() 
Converts this string to a new character array.
40 String toLowerCase()
Converts all of the characters in this String to lower case using the rules of the default locale.
41 String toLowerCase(Locale locale)
将所有的在这个字符串中的字符为大写使用的默认语言环境的规则。
42 String toString()
This object (which is already a string!) is itself returned.
43 String toUpperCase() 
Converts all of the characters in this String to upper case using the rules of the default locale.
44 String toUpperCase(Locale locale) 
Converts all of the characters in this String to upper case using the rules of the given Locale.
45 String trim() 
Returns a copy of the string, with leading and trailing whitespace omitted.
46 static String valueOf(primitive data type x) 
Returns the string representation of the passed data type argument.
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