Java Regex中matches()和find()之间的区别

Question

我想明白之间的差别matches()和find().

根据Javadoc(根据我的理解),matches()即使它找到了它正在寻找的东西,它也会搜索整个字符串,并find()在它找到它所寻找的内容时停止.

如果这个假设是正确matches()的find(),除非你想要计算它找到的匹配数,否则我无法看到你想要使用的代替.

在我看来,String类应该具有find()而不是matches()作为内置方法.

总结一下:

1. 我的假设是否正确？
2. 何时使用matches()而不是find()？

Answer 1

matches尝试将表达式与整个字符串进行匹配,^并$在模式的开头和结尾隐式添加a ,这意味着它不会查找子字符串.因此,此代码的输出:

public static void main(String[] args) throws ParseException {
    Pattern p = Pattern.compile("\\d\\d\\d");
    Matcher m = p.matcher("a123b");
    System.out.println(m.find());
    System.out.println(m.matches());

    p = Pattern.compile("^\\d\\d\\d$");
    m = p.matcher("123");
    System.out.println(m.find());
    System.out.println(m.matches());
}

/* output:
true
false
true
true
*/

123是一个子串,a123b所以find()方法输出true.matches()只有'看'与a123b它不相同123,因而输出错误.

Answer 2

matches如果整个字符串与给定模式匹配,则返回true.find尝试查找与模式匹配的子字符串.

Answer 3

matches()只有匹配完整的字符串才会返回true. find()将尝试在与正则表达式匹配的子字符串中查找下一个匹配项.注意强调"下一个".这意味着,find()多次调用的结果可能不一样.此外,通过使用,find()您可以调用start()以返回子字符串匹配的位置.

final Matcher subMatcher = Pattern.compile("\\d+").matcher("skrf35kesruytfkwu4ty7sdfs");
System.out.println("Found: " + subMatcher.matches());
System.out.println("Found: " + subMatcher.find() + " - position " + subMatcher.start());
System.out.println("Found: " + subMatcher.find() + " - position " + subMatcher.start());
System.out.println("Found: " + subMatcher.find() + " - position " + subMatcher.start());
System.out.println("Found: " + subMatcher.find());
System.out.println("Found: " + subMatcher.find());
System.out.println("Matched: " + subMatcher.matches());

System.out.println("-----------");
final Matcher fullMatcher = Pattern.compile("^\\w+$").matcher("skrf35kesruytfkwu4ty7sdfs");
System.out.println("Found: " + fullMatcher.find() + " - position " + fullMatcher.start());
System.out.println("Found: " + fullMatcher.find());
System.out.println("Found: " + fullMatcher.find());
System.out.println("Matched: " + fullMatcher.matches());
System.out.println("Matched: " + fullMatcher.matches());
System.out.println("Matched: " + fullMatcher.matches());
System.out.println("Matched: " + fullMatcher.matches());

将输出:

Found: false
Found: true - position 4
Found: true - position 17
Found: true - position 20
Found: false
Found: false
Matched: false
-----------
Found: true - position 0
Found: false
Found: false
Matched: true
Matched: true
Matched: true
Matched: true

因此,find()如果Matcher未重置对象,则多次调用时要小心,即使正则表达式被包围^并$匹配完整字符串也是如此.

Answer 4

find()将考虑针对正则表达式的子字符串，matches()将视为完整表达式。

find() 仅当表达式的子字符串与模式匹配时才返回true。

public static void main(String[] args) {
        Pattern p = Pattern.compile("\\d");
        String candidate = "Java123";
        Matcher m = p.matcher(candidate);

        if (m != null){
            System.out.println(m.find());//true
            System.out.println(m.matches());//false
        }
    }