java中split() replace() replaceAll()三个函数分析

本文系转载，转自：http://feigme.iteye.com/blog/147259

java.lang.String split

    String value = "a,b,c,d,e";
    String[] names = value.split(",");
    for(int i=0,n=names.length;i
    System.out.print(names[i]);
    } 

运行结果：

a b c d e

但是在做ip解析时发现出了问题，代码如下：

    String value = "209.242.1.1";
    String[] names = value.split(".");
    for(int i=0,n=names.length;i
    System.out.print(names[i]+" ");
    } 

理想的输出结果应该是219 242 1 1，结果什么都没有输出。

很奇怪哦。看一下split的方法签名吧。

    public String[] split(String regex) 

这里的参数的名称是regex ，也就是 Regular Expression（正则表达式）。这个参数并不是一个简单的分割用的字符，而是一个正则表达式：

    public String[] split(String regex, int limit) {
    return Pattern.compile(regex).split(this, limit);
    } 

split 的实现直接调用的 Matcher 类的 split 的方法。“. ”在正则表达式中有特殊的含义，因此我们使用的时候必须进行转义。

修改代码如下：

    String value = "209.242.1.1";
    String[] names = value.split("\\.");
    for(int i=0,n=names.length;i
    System.out.print(names[i]+" ");
    } 

    String java.lang.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.

    @Test
    public void testReplace(){
    String A = "aaa bCskd dkkAik kdaFe";
    System.out.println(A.replace('a', '_'));
    }

    @Test
    public void testReplace(){
    String A = "aaa bCskd dkkAik kaaaFe";
    System.out.println(A.replace("aaa", "="));
    }

String java.lang.String.replace(CharSequence target, CharSequence replacement)
Replaces each substring of this string that matches the literal target sequence
with the specified literal replacement sequence. The replacement proceeds from
the beginning of the string to the end, for example, replacing "aa" with "b" in
the string "aaa" will result in "ba" rather than "ab".
Parameters:
target The sequence of char values to be replaced
replacement The replacement sequence of char values
Returns:
The resulting string
Throws:
NullPointerException if target or replacement is null.
Since:
1.5

    @Test
    public void testReplace(){
    String A = "aaa bCskd dkkAik kaaaFe";
    System.out.println(A.replace(" ", ""));
    } 

    @Test
    public void testReplace(){
    String A = "aaa bCskd dkkAik kaaaFe";
    System.out.println(A.replaceAll("[a-z]", "="));
    } 

    String java.lang.String.replaceAll(String regex, String replacement)
    Replaces each substring of this string that matches the given regular expression
    with the given replacement.
    An invocation of this method of the form str.replaceAll(regex, repl) yields exactly
    the same result as the expression
    java.util.regex.Pattern. compile(regex).java.util.regex.Pattern.matcher(java.lang.CharSequence) matcher(str). replaceAll(repl)
    See Also:
    java.util.regex.Pattern
    Parameters:
    regex the regular expression to which this string is to be matched
    Returns:
    The resulting String
    Throws:
    PatternSyntaxException if the regular expression's syntax is invalid
    Since:
    1.4
    @spec
    JSR-51