不使用正则表达式：

import java.util.Scanner;

public class RagexDemo01 {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String str = scanner.next();

        boolean flag = true;

        char[] c = str.toCharArray();

        for (int i = 0; i < c.length; i++) {

            if (c[i] < '0' || c[i] > '9') {

                flag = false;

                System.out.println("fffffffff");

                break;

            }

        }

        if (flag) {

            System.out.println("All is number!");

        } else {

            System.out.println("Not all is number!");

        }

    }

}

使用正则表达式：

import java.util.Scanner;

import java.util.regex.Pattern;

public class RegexDemo02 {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String string = scanner.next();

        if (Pattern.compile("[0-9]+").matcher(string).matches()) {

            System.out.println("ALL IS NUM!");

        } else {

            System.out.println("NOT ALL IS NUM!");

        }

    }

}

如果要在程序中应用正则表达式则必须依靠Pattern类与Matcher类，这两个类都在java.util.regex包中定义。Pattern类的主要作用是进行正则规范的编写，而Matcher类主要是执行规范，验证一个字符串是否符合其规范。

 

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class RegexDemo03 {

    public static void main(String[] args) {

        String str = "19W3-12-51";

        String pat = "\\d{4}-\\d{2}-\\d{2}";

        Pattern p = Pattern.compile(pat);

        Matcher m = p.matcher(str);

        if (m.matches()) {

            System.out.println("OKKKKKK!");

        } else {

            System.out.println("NOOOOOO!");

        }

    }

}

 

按数字拆分字符串：

public class RegexDemo04 {

    public static void main(String[] args) {

        String str = "A1BFOEIWOEF02223IOFEJW09323";

        String pat = \\d;  // \d 代表数字

        Pattern p = Pattern.compile(pat);

        String s[] = p.split(str);

        for (int x = 0; x < s.length; x++) {

            System.out.println(s[x] + "\t");

        }

    }

}

替换所有数字为#：

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class RegexDemo05 {

    public static void main(String[] args) {

        String str = "A1B32GEJO31BFEO231NFE";

        String pat = "\\d+";

        Pattern p = Pattern.compile(pat);

        Matcher m = p.matcher(str);

        String newString = m.replaceAll("#");

        System.out.println(newString);

    }

}

直接使用string类的支持正则表达式的方法：

public class RegexDemo06 {

    public static void main(String[] args) {

        String str1 = "A3OFE21FAFEO23FAF321".replaceAll("\\d", "#");

        boolean temp = "1932-32-12".matches("\\d{4}-\\d{2}-\\d{2}");

        String s[] = "A1L309LFE233202FAG21LF".split("\\d+");

        System.out.println(str1);

        System.out.println(temp);

        for (int x = 0; x < s.length; x++) {

            System.out.println(s[x] + "\t");

        }

    }

}