Java 中的正则表达式
原文:https://www.geeksforgeeks.org/regular-expressions-in-java/
正则表达式(简称 Regex)是一个定义字符串模式的应用编程接口，可用于在 Java 中搜索、操作和编辑字符串。电子邮件验证和密码是字符串的几个领域，Regex 被广泛用于定义约束。正则表达式在 java.util.regex 包下提供。这包括 3 个类和 1 个接口。Java . util . regex包主要由以下三个类组成，如下表所示:
对文本执行匹配操作 | kind | describe | | --- | --- | | 乌提尔。regex。模式 | Used to define patterns. | | 不，不，不。瑞吉斯。匹配项 | Used for usage mode |Java 中的 Regex 为我们提供了下面列出的两个类:
- 模式类
- 火柴人班
更多的理解可以从下面提供的图片中理解如下:
类 1: 模式类
此类是正则表达式的编译，可用于定义各种类型的模式，不提供公共构造函数。这可以通过调用 compile()方法来创建，该方法接受正则表达式作为第一个参数，从而在执行后返回一个模式。
| way | describe | | --- | --- | | 编译(字符串正则表达式) | It is used to compile a given regular expression into a pattern. | | 年复一年(regex 字符串，int flags) | Used to compile a given regular expression into a pattern with a given flag. | | 旗帜() | The matching flag used to return the pattern. | | 匹配器(字符序列输入) | It is used to create a matcher that will match the given input according to the pattern. | | 匹配(字符串正则表达式，字符序列输入) | It is used to compile the given regular expression and try to match the given input with it. | | model | Returns the regular expression used to compile the pattern. | | quote | The text pattern string used to return the specified string. | | 拆分(字符序列输入) | Used to split the given input sequence around the matches of the pattern. | | 拆分(CharSequence 输入，int 限制) | Used to split the given input sequence around the matches of the pattern. Limit the number of times the parameter controls the application mode. | | toString() | It is used to return the string representation of this pattern. |示例:模式类
Java 语言(一种计算机语言，尤用于创建网站)
// Java Program Demonstrating Working of matches() Method
// Pattern class
// Importing Pattern class from java.util.regex package
import java.util.regex.Pattern;
// Main class
class GFG {
// Main driver method
public static void main(String args[])
{
// Following line prints "true" because the whole
// text "geeksforgeeks" matches pattern
// "geeksforge*ks"
System.out.println(Pattern.matches(
"geeksforge*ks", "geeksforgeeks"));
// Following line prints "false" because the whole
// text "geeksfor" doesn't match pattern "g*geeks*"
System.out.println(
Pattern.matches("g*geeks*", "geeksfor"));
}
}
Output
true
false
2 级:火柴人级
该对象用于在 java 中对输入字符串执行匹配操作，从而解释前面解释的模式。这也没有定义公共构造函数。这可以通过在任何模式对象上调用 matcher()来实现。
| way | describe | | --- | --- | | 查找() | It is mainly used to search for regular expressions that appear many times in text. | | 查找(int start) | Used to search for the occurrence of regular expressions in text from a given index. | | 【开始()】 | Gets the starting index of the match found using the find () method. | | end() | Gets the ending index of the match found using the find () method. It returns the character index next to the last matching character. | | 组计数() | Total number of matching subsequences used to find. | | Group () | Used to find matching subsequences. | | matching | Used to test whether the regular expression matches the pattern. |注意:【Pattern.matches()检查整个文本是否与模式匹配。其他方法(如下所示)主要用于查找文本中模式的多次出现。
让我们像讨论模式类一样讨论几个示例程序。为了更好地理解 Matcher 类，这里我们将讨论几个演示 compile()、find()、start()、end()和 split()工作原理的 java 程序。
示例 1: 模式搜索
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate working of
// String matching in Java
// Importing Matcher and Pattern class to
//
import java.util.regex.Matcher;
import java.util.regex.Pattern;
// Main class
class GFG {
// Main driver method
public static void main(String args[])
{
// Create a pattern to be searched
// Custom pattern
Pattern pattern = Pattern.compile("geeks");
// Search above pattern in "geeksforgeeks.org"
Matcher m = pattern.matcher("geeksforgeeks.org");
// Finding string using find() method
while (m.find())
// Print starting and ending indexes
// of the pattern in the text
// using this functionality of this class
System.out.println("Pattern found from "
+ m.start() + " to "
+ (m.end() - 1));
}
}
Output
Pattern found from 0 to 4
Pattern found from 8 to 12
示例 2: 简单正则表达式搜索
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate working of
// String matching in Java
// Importing Matcher and Pattern class
// from java.util package
import java.util.regex.Matcher;
import java.util.regex.Pattern;
// Main class
class GFG {
// Main driver method
public static void main(String args[])
{
// Creating a pattern to be searched
// Custom pattern to be searched
Pattern pattern = Pattern.compile("ge*");
// Searching for the above pattern in
// "geeksforgeeks.org"
Matcher m = pattern.matcher("geeksforgeeks.org");
// Checking whether the pattern is there or not
// using find() method
while (m.find())
// Print starting and ending indexes of the
// pattern in text using method functionality of
// this class
System.out.println("Pattern found from "
+ m.start() + " to "
+ (m.end() - 1));
}
}
Output
Pattern found from 0 to 2
Pattern found from 8 to 10
Pattern found from 16 to 16
示例 3: 不区分大小写的模式搜索
Java 语言(一种计算机语言，尤用于创建网站)
// Java Program Demonstrating Working of String matching
// Importing Matcher class and Pattern classes
// from java.util.regex package
import java.util.regex.Matcher;
import java.util.regex.Pattern;
// Main class
class GFG {
// Main driver method
public static void main(String args[])
{
// Creating a pattern to be searched
Pattern pattern = Pattern.compile(
"ge*", Pattern.CASE_INSENSITIVE);
// Searching above pattern in "geeksforgeeks.org"
Matcher m = pattern.matcher("GeeksforGeeks.org");
// Find th above string using find() method
while (m.find())
// Printing the starting and ending indexes of
// the pattern in text using class method
// functionalities
System.out.println("Pattern found from "
+ m.start() + " to "
+ (m.end() - 1));
}
}
Output
Pattern found from 0 to 2
Pattern found from 8 to 10
Pattern found from 16 to 16
示例 4: split()方法根据分隔符模式拆分文本。
string split()方法在给定正则表达式的匹配项周围断开给定的字符串。这种方法有两种变体，所以在开始实现这种方法之前一定要仔细研究一下。
插图:
Input --> String: 016-78967
Output --> Regex: {"016", "78967"}
Java 语言(一种计算机语言，尤用于创建网站)
// Java program Illustrating Working of split() Method
// by Splitting a text by a given pattern
// Importing Matcher and Pattern classes from
// java.util.regex package
import java.util.regex.Matcher;
import java.util.regex.Pattern;
// Main class
class GFG {
// Main driver method
public static void main(String args[])
{
// Custom string
String text = "geeks1for2geeks3";
// Specifies the string pattern
// which is to be searched
String delimiter = "\\d";
Pattern pattern = Pattern.compile(
delimiter, Pattern.CASE_INSENSITIVE);
// Used to perform case insensitive search of the
// string
String[] result = pattern.split(text);
// Iterating using for each loop
for (String temp : result)
System.out.println(temp);
}
}
Output
geeks
for
geeks
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