Java-正则表达式

主要功能方法举例

1.判断功能

验证键盘输入QQ号码是否格式正确（体现正则表达式的优势）
格式要求：非0开头，5-11位

public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入QQ号码：");
        String s = sc.next();
        //boolean falg = checkQQNumber(s);//if语句判断qq号码格式
        boolean falg = checkQQNumber1(s);//正则表达式判断qq号码格式
        if (falg == true){
            System.out.println("输入号码正确");
        }else
            System.out.println("输入号码错误");
    }
    
    private static boolean checkQQNumber(String s) {
        boolean flag = false;
        if (s.length()>= 5&&s.length()<= 12){
            if (!s.startsWith("0")){
                for (int i = 1; i < s.length(); i++) {
                    char c = s.charAt(i);
                    if (!(c>='0'&&c<='9')){
                        return flag;
                    }
                }
                flag = true;
            }
        }
        return flag;
    }
    
    private static boolean checkQQNumber1(String s) {
        boolean matches = s.matches("[1-9][0-9]{4,11}");
        return matches;
    }

2.分割功能

将字符串"11 22 88 99 77 66 55"排序后输出
输出结果："11 22 55 66 77 88 99"

public class Split {
    public static void main(String[] args) {
        String s = "11 22 88 99 77 66 55";
        String[] strings = s.split(" ");//根据空格分割字符串
        int[] ints = new int[strings.length];
        //将分割出的字符串数组元素放进int数组中用来排序
        for (int i = 0; i < ints.length; i++) {
            ints[i] = Integer.parseInt(strings[i]);
        }
        //排序
        Arrays.sort(ints);
        //再将排序好的元素组成字符串输出
        StringBuilder stringBuilder = new StringBuilder();
        for (int i = 0; i < ints.length; i++) {
            stringBuilder.append(ints[i]).append(" ");
        }
        System.out.println(stringBuilder.toString().trim());
    }
}

3.替换功能

去除字符串中出现的空格

String str="abc      abcabcabc  abc        abc";
String s = str.replaceAll(" +", "");
System.out.println(s);//输出结果：abcabcabcabcabcabc