Guava base -- CharMatcher

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Guava全文介绍地址:Google Guava
这次主要介绍是的是com.google.common.base.CharMatcher。决定一些Java中char类型的值是true还是false，就好像Predicate对于Object类型一样。还提供基于此函数的基本文本处理方法。强烈建议实现无副作用和不可变的。
注意:这个类仅仅处理char类型的值。它不理解补充在范围为(0x10000 - 0x10FFFF)Unicode码。这样的逻辑使用代理对字符编码成一个字符串,和CharMatcher对待这些就像两个不同的字符。

由于这个类方法比较多，我就说它几个常用的方法。你就可以根据这几个方法推及到其它用法。它的常用所有方法如下:

String replaceFrom(CharSequence sequence, char replacement)返回一个String类型,替换掉目标sequence中符合CharMatcher类型的值为给定的replacementString replaceFrom(CharSequence sequence, CharSequence replacement)返回一个String类型,替换掉目标sequence中符合CharMatcher类型的值为给定的replacementStringcollapseFrom(CharSequence sequence, char replacement)返回一个String类型,替换目标sequence中每个组的连续字符匹配这匹配器取代了一个替换字符注意：它只会替换字符中间的，如果这个字符前面有对应的它就会报错eg.   String a = "  aaa    bbb     cccc";      String b = "aaa   bbb    ccc";  CharMatcher.WHITESPACE.collapseFrom(a, " ");// 会报错  CharMatcher.WHITESPACE.collapseFrom(b, " ");// result : "aaa bbb ccc";  String trimAndCollapseFrom(CharSequence sequence, char replacement)返回一个String类型,替换目标sequence中每个组的连续字符匹配这匹配器取代了一个替换字符(不只是中间前面对应的 CharMatcher也会被替换掉)String trimAndCollapseFrom(CharSequence sequence, char replacement)返回一个String类型,替换目标sequence中每个组的连续字符匹配这匹配器取代了一个替换字符(不只是中间前面对应的 CharMatcher也会被替换掉)String retainFrom(CharSequence sequence)返回一个String类型，提取目标sequence中包含CharMatcher的所有字符序列StringretainFrom(CharSequence sequence)其中包含所有在秩序中匹配字符的字符序列。

然后大家就可以对照下面的例子来理解这个类的用法了。

public class CharMatcherTest {    @Test    public void testRemoveLinebreaks(){        String stringWithLinebreaks = "This is an example\n"+                                      "of a String with linebreaks\n"+                                      "we want on one line";        String expected = "This is an example of a String with linebreaks we want on one line";        String scrubbed = CharMatcher.BREAKING_WHITESPACE.replaceFrom(stringWithLinebreaks,' ');        assertThat(scrubbed,is(expected));    }    @Test    public void testRemoveWhiteSpace(){        String tabsAndSpaces = "String  with      spaces     and           tabs";        String expected = "String with spaces and tabs";        String scrubbed = CharMatcher.WHITESPACE.collapseFrom(tabsAndSpaces,' ');        assertThat(scrubbed,is(expected));    }    @Test    public void testTrimRemoveWhiteSpace(){        String tabsAndSpaces = "    String  with      spaces     and           tabs";        String expected = "String with spaces and tabs";        String scrubbed = CharMatcher.WHITESPACE.trimAndCollapseFrom(tabsAndSpaces,' ');        assertThat(scrubbed,is(expected));    }    @Test    public void testRetainFrom(){        String lettersAndNumbers = "foo989yxbar234";        String expected = "989234";        String retained = CharMatcher.JAVA_DIGIT.retainFrom(lettersAndNumbers);        assertThat(expected,is(retained));    }    @Test    public void testCombineMatchers(){        CharMatcher cm = CharMatcher.inRange('A','E');        assertThat(cm.retainFrom("aaaABbbccCdddDEeee"),is("ABCDE"));    }}

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