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news 来源：原创 2024/5/16 4:04:53

2019独角兽企业重金招聘Python工程师标准>>>

1.”UTF-8″必须在Java平台中被支持 2.人工敲入会有偏差

// byte[] bytes = "foo".getBytes("UTF-8");
// 解决： Charsets类提供了对Java平台支持字符集
byte[] bytes = "foo".getBytes(Charsets.UTF_8);

2.使用StringBuilder类连接字符串太繁琐，代码其实都是重复的

//解决： Strings类封装了连接字符串的统一代码
String stringsTest = Strings.padEnd("foo", 6, 'o');
System.out.println(stringsTest);

3.在String作为参数时，将null转换成””防止空指针问题

String nullToEmptyTest1 = Strings.nullToEmpty("123");
String nullToEmptyTest2 = Strings.nullToEmpty(null);
System.out.println(nullToEmptyTest1 + "--" + nullToEmptyTest2);

4.””转null

String emptyToNullTest1 = Strings.emptyToNull("123");
String emptyToNullTest2 = Strings.emptyToNull("");
System.out.println(emptyToNullTest1 + "--" + emptyToNullTest2);

5将字符串中的Tab和多个空格转为一个空格

String tabsAndSpaces = "String with   spaces    and tabs";
String expected = "String with spaces and tabs";
String scrubbed = CharMatcher.WHITESPACE.collapseFrom(tabsAndSpaces,' ');
System.out.println(expected.equals(scrubbed));

6Object utilities 对象工具

// 1. toString()实现
System.out.println(Objects.toStringHelper(WorkingWithStrings.class).omitNullValues()
.add("expected", expected).add("tabsAndSpaces", tabsAndSpaces));
// 2. 检查如果为null值 , 填充默认值
System.out.println(Objects.firstNonNull(null, "default value"));
// 3. 生成hashcode
System.out.println(Objects.hashCode(tabsAndSpaces, expected));
// 4. CompareTo实现    如果都是相同的返回0，有一个不同返回-1
System.out.println(ComparisonChain.start().compare(tabsAndSpaces, expected).compare(expected, scrubbed).result());
}

7 emptyTonull

public void testEmptyToNull() {
assertNull(Strings.emptyToNull(null));
assertNull(Strings.emptyToNull(""));
assertEquals("a", Strings.emptyToNull("a"));
}

判断是否为空

public void testIsNullOrEmpty() {
assertTrue(Strings.isNullOrEmpty(null));
assertTrue(Strings.isNullOrEmpty(""));
assertFalse(Strings.isNullOrEmpty("a"));
}

补全字符串(向前追加) 第一个参数是要补全的字符串，第二个是最终字符串长度第三个是要拿什么字符补全

public void testPadStart_noPadding() {
assertSame("", Strings.padStart("", 0, '-'));
assertSame("x", Strings.padStart("x", 0, '-'));
assertSame("x", Strings.padStart("x", 1, '-'));
assertSame("xx", Strings.padStart("xx", 0, '-'));
assertSame("xx", Strings.padStart("xx", 2, '-'));
}
public void testPadStart_somePadding() {
assertEquals("-", Strings.padStart("", 1, '-'));
assertEquals("--", Strings.padStart("", 2, '-'));
assertEquals("-x", Strings.padStart("x", 2, '-'));
assertEquals("--x", Strings.padStart("x", 3, '-'));
assertEquals("-xx", Strings.padStart("xx", 3, '-'));
}

补全字符串(向后追加) 第一个参数是要补全的字符串，第二个是最终字符串长度第三个是要拿什么字符补全

 public void testPadEnd_noPadding() {
assertSame("", Strings.padEnd("", 0, '-'));
assertSame("x", Strings.padEnd("x", 0, '-'));
assertSame("x", Strings.padEnd("x", 1, '-'));
assertSame("xx", Strings.padEnd("xx", 0, '-'));
assertSame("xx", Strings.padEnd("xx", 2, '-'));
}
public void testPadEnd_somePadding() {
assertEquals("-", Strings.padEnd("", 1, '-'));
assertEquals("--", Strings.padEnd("", 2, '-'));
assertEquals("x-", Strings.padEnd("x", 2, '-'));
assertEquals("x--", Strings.padEnd("x", 3, '-'));
assertEquals("xx-", Strings.padEnd("xx", 3, '-'));
}

重复某个字符串几次Watch Full Movie Online Streaming Online and Download

    String input = "20";
assertEquals("", Strings.repeat(input, 0));
assertEquals("20", Strings.repeat(input, 1));
assertEquals("2020", Strings.repeat(input, 2));
assertEquals("202020", Strings.repeat(input, 3));
assertEquals("", Strings.repeat("", 4));

返回两个字符串相同的头部分内容

assertEquals("", Strings.commonPrefix("", ""));
assertEquals("", Strings.commonPrefix("abc", ""));
assertEquals("", Strings.commonPrefix("", "abc"));
assertEquals("", Strings.commonPrefix("abcde", "xyz"));
assertEquals("", Strings.commonPrefix("xyz", "abcde"));
assertEquals("", Strings.commonPrefix("xyz", "abcxyz"));
assertEquals("a", Strings.commonPrefix("abc", "aaaaa"));
assertEquals("aa", Strings.commonPrefix("aa", "aaaaa"));
assertEquals("abc",
Strings.commonPrefix(new StringBuffer("abcdef"), "abcxyz"));
// Identical valid surrogate pairs.
assertEquals("abc\uD8AB\uDCAB",
Strings.commonPrefix("abc\uD8AB\uDCABdef", "abc\uD8AB\uDCABxyz"));
// Differing valid surrogate pairs.
assertEquals("abc",
Strings.commonPrefix("abc\uD8AB\uDCABdef", "abc\uD8AB\uDCACxyz"));
// One invalid pair.
assertEquals("abc",
Strings.commonPrefix("abc\uD8AB\uDCABdef", "abc\uD8AB\uD8ABxyz"));
// Two identical invalid pairs.
assertEquals("abc\uD8AB\uD8AC",
Strings.commonPrefix("abc\uD8AB\uD8ACdef", "abc\uD8AB\uD8ACxyz"));
// Two differing invalid pairs.
assertEquals("abc\uD8AB",
Strings.commonPrefix("abc\uD8AB\uD8ABdef", "abc\uD8AB\uD8ACxyz"));
// One orphan high surrogate.
assertEquals("", Strings.commonPrefix("\uD8AB\uDCAB", "\uD8AB"));
// Two orphan high surrogates.
assertEquals("\uD8AB", Strings.commonPrefix("\uD8AB", "\uD8AB"));

返回两个字符串结尾相同的部分

assertEquals("", Strings.commonSuffix("", ""));
assertEquals("", Strings.commonSuffix("abc", ""));
assertEquals("", Strings.commonSuffix("", "abc"));
assertEquals("", Strings.commonSuffix("abcde", "xyz"));
assertEquals("", Strings.commonSuffix("xyz", "abcde"));
assertEquals("", Strings.commonSuffix("xyz", "xyzabc"));
assertEquals("c", Strings.commonSuffix("abc", "ccccc"));
assertEquals("aa", Strings.commonSuffix("aa", "aaaaa"));
assertEquals("abc",
Strings.commonSuffix(new StringBuffer("xyzabc"), "xxxabc"));
// Identical valid surrogate pairs.
assertEquals("\uD8AB\uDCABdef",
Strings.commonSuffix("abc\uD8AB\uDCABdef", "xyz\uD8AB\uDCABdef"));
// Differing valid surrogate pairs.
assertEquals("def",
Strings.commonSuffix("abc\uD8AB\uDCABdef", "abc\uD8AC\uDCABdef"));
// One invalid pair.
assertEquals("def",
Strings.commonSuffix("abc\uD8AB\uDCABdef", "xyz\uDCAB\uDCABdef"));
// Two identical invalid pairs.
assertEquals("\uD8AB\uD8ABdef",
Strings.commonSuffix("abc\uD8AB\uD8ABdef", "xyz\uD8AB\uD8ABdef"));
// Two differing invalid pairs.
assertEquals("\uDCABdef",
Strings.commonSuffix("abc\uDCAB\uDCABdef", "abc\uDCAC\uDCABdef"));
// One orphan low surrogate.
assertEquals("", Strings.commonSuffix("x\uD8AB\uDCAB", "\uDCAB"));
// Two orphan low surrogates.
assertEquals("\uDCAB", Strings.commonSuffix("\uDCAB", "\uDCAB"));

validSurrogatePairAt 方法来判断最后两个字符是不是合法的 “Java 平台增补字符”

public void testValidSurrogatePairAt() {
assertTrue(Strings.validSurrogatePairAt("\uD8AB\uDCAB", 0));
assertTrue(Strings.validSurrogatePairAt("abc\uD8AB\uDCAB", 3));
assertTrue(Strings.validSurrogatePairAt("abc\uD8AB\uDCABxyz", 3));
assertFalse(Strings.validSurrogatePairAt("\uD8AB\uD8AB", 0));
assertFalse(Strings.validSurrogatePairAt("\uDCAB\uDCAB", 0));
assertFalse(Strings.validSurrogatePairAt("\uD8AB\uDCAB", -1));
assertFalse(Strings.validSurrogatePairAt("\uD8AB\uDCAB", 1));
assertFalse(Strings.validSurrogatePairAt("\uD8AB\uDCAB", -2));
assertFalse(Strings.validSurrogatePairAt("\uD8AB\uDCAB", 2));
assertFalse(Strings.validSurrogatePairAt("x\uDCAB", 0));
assertFalse(Strings.validSurrogatePairAt("\uD8ABx", 0));
}
//这个方法请看源码：
@VisibleForTesting
static boolean validSurrogatePairAt(CharSequence string, int index) {
return index >= 0
&& index <= (string.length() - 2)
&& Character.isHighSurrogate(string.charAt(index))
&& Character.isLowSurrogate(string.charAt(index + 1));
}

转载于:https://my.oschina.net/u/1024107/blog/868337