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  • java之Pattern类详解

    在JDK 1.4中,Java增加了对正则表达式的支持。

    java与正则相关的工具主要在java.util.regex包中;此包中主要有两个类:PatternMatcher


    Pattern 

    声明:public final class Pattern  implements java.io.Serializable

    Pattern类有final 修饰,可知他不能被子类继承。

    含义:模式类,正则表达式的编译表示形式。

    注意:此类的实例是不可变的,可供多个并发线程安全使用。


    字段:

    复制代码
     public static final int UNIX_LINES = 0x01;
    
        /**
         * 启用不区分大小写的匹配。*/
        public static final int CASE_INSENSITIVE = 0x02;
    
        /**
         * 模式中允许空白和注释。
         */
        public static final int COMMENTS = 0x04;
    
        /**
         * 启用多行模式。
         */
        public static final int MULTILINE = 0x08;
    
        /**
         * 启用模式的字面值解析。*/
        public static final int LITERAL = 0x10;
    
        /**
         * 启用 dotall 模式。
         */
        public static final int DOTALL = 0x20;
    
        /**
         * 启用 Unicode 感知的大小写折叠。*/
        public static final int UNICODE_CASE = 0x40;
    
        /**
         *  启用规范等价。
         */
        public static final int CANON_EQ = 0x80;
        private static final long serialVersionUID = 5073258162644648461L;
    
        /**
         * The original regular-expression pattern string.
         */
        private String pattern;
    
        /**
         * The original pattern flags.
         */
        private int flags;
    
        /**
         * Boolean indicating this Pattern is compiled; this is necessary in order
         * to lazily compile deserialized Patterns.
         */
        private transient volatile boolean compiled = false;
    
        /**
         * The normalized pattern string.
         */
        private transient String normalizedPattern;
    
        /**
         * The starting point of state machine for the find operation.  This allows
         * a match to start anywhere in the input.
         */
        transient Node root;
    
        /**
         * The root of object tree for a match operation.  The pattern is matched
         * at the beginning.  This may include a find that uses BnM or a First
         * node.
         */
        transient Node matchRoot;
    
        /**
         * Temporary storage used by parsing pattern slice.
         */
        transient int[] buffer;
    
        /**
         * Temporary storage used while parsing group references.
         */
        transient GroupHead[] groupNodes;
    
        /**
         * Temporary null terminated code point array used by pattern compiling.
         */
        private transient int[] temp;
    
        /**
         * The number of capturing groups in this Pattern. Used by matchers to
         * allocate storage needed to perform a match.此模式中的捕获组的数目。
         */
        transient int capturingGroupCount;
    
        /**
         * The local variable count used by parsing tree. Used by matchers to
         * allocate storage needed to perform a match.
         */
        transient int localCount;
    
        /**
         * Index into the pattern string that keeps track of how much has been
         * parsed.
         */
        private transient int cursor;
    
        /**
         * Holds the length of the pattern string.
         */
        private transient int patternLength;
    复制代码

    组和捕获

    捕获组可以通过从左到右计算其开括号来编号。

    在表达式 ((A)(B(C))) 中,存在四个组: 

    1 ABC
    2 A
    3 BC
    4 C

    组零始终代表整个表达式。 


    构造器

    复制代码
        private Pattern(String p, int f) {
            pattern = p;
            flags = f;
    
            // Reset group index count
            capturingGroupCount = 1;
            localCount = 0;
    
            if (pattern.length() > 0) {
                compile();
            } else {
                root = new Start(lastAccept);
                matchRoot = lastAccept;
            }
        }
    复制代码

    构造器是私有的,可知不能通过new创建Pattern对象。

    如何得到Pattern类的实例?

    查阅所有方法后发现:

        public static Pattern compile(String regex) {
            return new Pattern(regex, 0);
        }
        public static Pattern compile(String regex, int flags) {
            return new Pattern(regex, flags);
        }

    可知是通过Pattern调用静态方法compile返回Pattern实例。

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  • 原文地址:https://www.cnblogs.com/gengaixue/p/8066294.html
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