String特性 null测试 split测试 正则表达式使用

一、String特性

1、不支持多行字符串；

2、实现CharSequence只读字符序列接口；

3、replace替换所有字符串；

4、replaceAll替换所有正则表达式；

5、intern返回字符串池的等值对象；

二、null测试

public static void testNull() {
String str = null;
System.out.println(str);
System.out.println("string is " + str);
System.out.println(str + " is string");
System.out.println(String.format("format string %s", str));

str = "feinen";
System.out.println(str.equals(null));
}

输出：

null
string is null
null is string
format string null

false

三、split测试

public static void testSplit() {
String str = "";
String[] arr = str.split(";");
System.out.println(arr.length);

str = ";";
arr = str.split(";");
System.out.println(arr.length);

str = "1;";
arr = str.split(";");
System.out.println(arr.length);
}

输出：

1
0
1

四、正则表达式使用

1、\w表示单词字符[a-zA-Z_0-9]；

2、matches将整个输入序列与模式匹配；
3、lookingAt将输入序列从头开始与模式匹配；
4、find扫描输入序列以查找与模式匹配的下一个子序列；

public static void testRegex() {
Pattern pattern;
Matcher match;
String emails = "email is aa@webank.com or bb@webank.com";
pattern = Pattern.compile("[\\w][\\w-.]+@[\\w-.]+[\\w]");
match = pattern.matcher(emails);
while (match.find()) {
System.out.println(match.group(0));
System.out.println(match.start());
System.out.println(match.end());
}

pattern = Pattern.compile("email is aa@webank.com or bb@webank.com");
match = pattern.matcher(emails);
if (match.matches()) {
System.out.println(match.group(0));
System.out.println(match.start());
System.out.println(match.end());
}

pattern = Pattern.compile("email");
match = pattern.matcher(emails);
if (match.lookingAt()) {
System.out.println(match.group(0));
System.out.println(match.start());
System.out.println(match.end());
}

pattern = Pattern.compile("mail");
match = pattern.matcher(emails);
if (match.lookingAt()) {
System.out.println(match.group(0));
System.out.println(match.start());
System.out.println(match.end());
}
}

输出：

aa@webank.com
9
22
bb@webank.com
26
39
email is aa@webank.com or bb@webank.com
0
39
email
0
5