@Test

    public void testJdkJoin() {

        List<String> strList = Lists.newArrayList("1", "2", null, "3", "4");

        //字符串拼接，无法跳过空字符串

        String str = String.join(",", strList);

        Assert.assertEquals("1,2,3,4", str);

    }

    @Test

    public void testGuavaJoin() {

        List<String> strList = Lists.newArrayList("1", "2", null, "3", "4");

        //字符串拼接，跳过空字符串

        String str = Joiner.on(",").skipNulls().join(strList);

        Assert.assertEquals("1,2,3,4", str);

    }

    @Test

    public void testJdkSplit(){

        String str = "1,2,   3  ,,4,";

        //trimResults():去除空格，omitEmptyStrings()：删除空数组

        String[] strList = str.split(",");

        //  List<String> strList = Splitter.on(",").trimResults().omitEmptyStrings().splitToList(str);

        for (int i = 0; i < strList.length; i++) {

            String s = strList[i];

            System.out.println(s);

        }

        Assert.assertEquals(4,strList.length);

    }

    @Test

    public void testGuavaSplit(){

        String str = "1,2,   3  ,,4,";

        //trimResults():去除空格，omitEmptyStrings()：删除空数组

        List<String> strList = Splitter.on(",").trimResults().omitEmptyStrings().splitToList(str);

        strList.forEach(s -> System.out.println(s));

        Assert.assertEquals(4,strList.size());

    }

    @Test

    public void testSearch(){

        String str = "abcdef";

        //包含字符串cd

        Assert.assertEquals(true,str.contains("cd"));

        //查找以abc开头的字符串

        Assert.assertEquals(true,str.startsWith("abc"));

        //查找以def结尾的字符串

        Assert.assertEquals(true,str.endsWith("def"));

    }

    @Test

    public void testConversion(){

        String str = "abcdef";

        String newStr = str.replace("bcde","hello");

        System.out.println(newStr);

        Assert.assertEquals("ahellof",newStr);

        String str2 = "ABC    abc    123";

        //打印数字

        System.out.println(CharMatcher.digit().retainFrom(str2));

        //打印小写字母

        System.out.println(CharMatcher.javaLowerCase().retainFrom(str2));

        //打印大写字母

        System.out.println(CharMatcher.javaUpperCase().retainFrom(str2));

        //打印所有字母

        System.out.println(CharMatcher.javaLetter().retainFrom(str2));

        //将多余的空格替换成一个空格

        System.out.println(CharMatcher.whitespace().trimAndCollapseFrom(str2,' '));

        //统计出现的字母

        System.out.println(String.valueOf(CharMatcher.javaLetter().countIn(str2)));

    }

ahellof

123

abc

ABC

ABCabc

ABC abc 123

6