Java正则-String.matches的坑

Java正则-String.matches的坑

我想用String.matches匹配一行之中是否有特定的子串，结果死活出不来，我也在好多在线正则匹配的网上测试了，我正则表达式写的正确。查询了半天才知道，用String.matches匹配的正则，会在正则表达式前后加上^ $，是匹配整个大字符串是否满足正则表达式，而不会匹配到其中满足条件的子串！

//我的想法是以下2种都会成功匹配，其实是错误的
//以下2种的正则"abc"相当于"^abc$",所以结果false
boolean a = "abcd".matches("abc");
boolean b =Pattern.matches("abc", "abcd");
System.out.println(a);//false
System.out.println(b);//false

//而这种方法就能成功匹配出abcd中的abc
Pattern p=Pattern.compile("abc");  
Matcher m=p.matcher("abcd");  
while(m.find()){  
    System.out.println(m.group());//abc  
}

不解的是java api中Pattern.matches是这样说明的

public static boolean matches(String regex,
CharSequence input)
Compiles the given regular expression and attempts to match the given input against it.
An invocation of this convenience method of the form

Pattern.matches(regex, input);

behaves in exactly the same way as the expression

Pattern.compile(regex).matcher(input).matches()

If a pattern is to be used multiple times, compiling it once and reusing it will be more efficient than invoking this method each time.

Parameters:
regex - The expression to be compiled
input - The character sequence to be matched

官网说表现是一样的，可结果肯定是不一样的啊。

参考链接：stackoverflow