正则表达式--Pattern和Matcher方法（二）

Leefs 2019-12-25 AM 2293℃ 0条

# 正则表达式--Pattern和Matcher方法（二）

### 前言

有了上篇文章中对Pattern和Matcher方法的一些基本了解，本篇将讲述《Java编程思想》的第13.6.4小节Pattern和Matcher方法

### 示例一

下面的类可以用来测试正则表达式，看看它们能否匹配一个输入字符串。

**代码**

```java
//Allows you to easily try out regular expressions.
//{Args:abcabcabcdefabs "abc+" "(abc)+" "(abc){2,}"}
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class TestRegularExpression{
    public static void main(String[] args){

if(args.length<2){
            System.out.println("Usage:\njava TestregularExpression "+"characterSequence regularExpression+");
        }
        System.out.println("Input:\""+args[0]+"\"");
        for(String arg:args){
            System.out.println("RegularExpression:\""+arg+"\"");
            //compile 编译要匹配的字符串 ，编译要匹配的正则表达式
            Pattern p=Pattern.compile(arg);
            //matcher 匹配compile内的字符串 输入matcher的字符串是否匹配上面的正则表达式 并生成一个matcher对象
            Matcher m=p.matcher(args[0]);
            while(m.find()){//判断是否已经匹配完
                //输出匹配字符串和字符串的开始结束位置
                System.out.println("Match \""+m.group()+"\" at position "+m.start()+"-"+(m.end()-1));
            }
        }
    }
}
```

第一个控制台参数是将要用来搜索匹配的输入字符串，后面的一个或多个参数都是正则表达式,它们将被用来在输入的第一个字符串中查找匹配。

Pattern对象表示编译后的正则表达式。测这个例子我们可以看出，我们使用已编译的Pattern上的matcher()方法，加上一个输入字符串，从额共同创造了一个matcher对象，同时，Pattern类还提供了static方法：

```java
static boolean matches(String regex,CharSequence input)
```

该方法用于检查regex是否匹配整个CharSequence类型的input参数。编译后的pattern对象还提供了split（）方法，它从匹配了regex的地方分割输入的字符串，返回分割后的子字符串String数组。

通过调用Pattrern.mathder(）方法，并传入一个字符串参数，我们得到一个Matcher对象。使用Matcher上的方法，我们能够判断各种不同类型的匹配是否成功：

```java
boolean matches();
boolean lookingAt();
boolean find();
boolean find(int start);
```

其中的matches（）方法用来判断整个输入字符串是否匹配正确的正则表达式，而lookingAt()则用来判断该字符串（不必是整个字符串）的开始部分是否能够匹配模式。

### 示例2

```java
对字符串Java now has regular expressions验证下列正则表达式是否能够发现一个匹配：
^Java
\Breg.*
n.w\s+h(a|i)s
s?
s*
s+
s{4}
s{1}.
s{0,3}
```

**代码**

```java
public class StringTest10 {
    public static void main(String[] args) {
        String str = "Java now has regular expressions";
        for(String arg: args){
            Pattern p = Pattern.compile(arg);
            Matcher m = p.matcher(str);
            while(m.find()){
                System.out.println("Match \"" + m.group() +"\" at positions " + m.start() + "-" + (m.end()-1) );
            }
            System.out.println("\n");
        }
    }
}
```

**输出参数**

```java
^Java
\Breg.*
n.w\s+h(a|i)s
s?
s*
s+
s{4}
s{1}.
s{0,3}
```

**输出结果**

```java
Match "Java" at positions 0-3

Match "now has" at positions 5-11

Match "" at positions 0--1
Match "" at positions 1-0
Match "" at positions 2-1
Match "" at positions 3-2
Match "" at positions 4-3
Match "" at positions 5-4
Match "" at positions 6-5
Match "" at positions 7-6
Match "" at positions 8-7
Match "" at positions 9-8
Match "" at positions 10-9
Match "s" at positions 11-11
Match "" at positions 12-11
Match "" at positions 13-12
Match "" at positions 14-13
Match "" at positions 15-14
Match "" at positions 16-15
Match "" at positions 17-16
Match "" at positions 18-17
Match "" at positions 19-18
Match "" at positions 20-19
Match "" at positions 21-20
Match "" at positions 22-21
Match "" at positions 23-22
Match "" at positions 24-23
Match "" at positions 25-24
Match "s" at positions 26-26
Match "s" at positions 27-27
Match "" at positions 28-27
Match "" at positions 29-28
Match "" at positions 30-29
Match "s" at positions 31-31
Match "" at positions 32-31

Match "s" at positions 11-11
Match "ss" at positions 26-27
Match "s" at positions 31-31

Match "s " at positions 11-12
Match "ss" at positions 26-27

Match "" at positions 0--1
Match "" at positions 1-0
Match "" at positions 2-1
Match "" at positions 3-2
Match "" at positions 4-3
Match "" at positions 5-4
Match "" at positions 6-5
Match "" at positions 7-6
Match "" at positions 8-7
Match "" at positions 9-8
Match "" at positions 10-9
Match "s" at positions 11-11
Match "" at positions 12-11
Match "" at positions 13-12
Match "" at positions 14-13
Match "" at positions 15-14
Match "" at positions 16-15
Match "" at positions 17-16
Match "" at positions 18-17
Match "" at positions 19-18
Match "" at positions 20-19
Match "" at positions 21-20
Match "" at positions 22-21
Match "" at positions 23-22
Match "" at positions 24-23
Match "" at positions 25-24
Match "ss" at positions 26-27
Match "" at positions 28-27
Match "" at positions 29-28
Match "" at positions 30-29
Match "s" at positions 31-31
Match "" at positions 32-31
```

### 示例3

**题目**

```
适用正则表达式(?i)((^[aeiou])|(\\s+[aeiou]))\\w+?[aeiou]\\b匹配字符串Arline ate eight apples and one orange while Anita hadn't any。
```

**代码**

```java
public class StringTest11 {
    public static void main(String[] args) {
        Pattern p = Pattern.compile("(?i)((^[aeiou])|(\\s+[aeiou]))\\w+?[aeiou]\\b");
        Matcher m = p.matcher("Arline ate eight apples and one orange while Anita hadn't any");
        while(m.find()){
            System.out.println("Match \""+ m.group() + "\" at positions " + m.start() + "-" + (m.end() - 1));
        }
    }
}
```

**运行结果**

```java
Match "Arline" at positions 0-5
Match " ate" at positions 6-9
Match " one" at positions 27-30
Match " orange" at positions 31-37
Match " Anita" at positions 44-49
```

Matcher.find()方法可用来在CharSequence中查找多个匹配。

模式`\\w+`将字符串划分为单词。find()像迭代器那样前向遍历输入字符串。

标签: Java, Java编程思想, 字符串, 正则表达式

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