字符串的学习和练习

知识点

/* * indexOf() * lastIndexOj() * replace() * split() * charAt() * *subString()频率很高的方法.用来截取字符串 */public class StringClass {    public static void main(String[] args) {        String s = "   abcdefg  ";        String s1 = new String("a   b    c");        //字符串长度        System.out.println(s.length());        //trim方法.去掉字符串两边的空格        System.out.println(s.trim().length());        System.out.println(s1.length());        //trim不能去除中间的空格        System.out.println(s1.trim().length());        //截取字符串部分        String s2 = "再来一瓶";        System.out.println(s2.substring(2));        System.out.println(s2.substring(1,3));        //index找出指定字符的位置(索引).不只是找字符.也可以找串        //找到子字符在当前字符中的首字母的索引        String s3 = "2121abcdef21g";        System.out.println(s3.indexOf("cd"));        //Ascll码也是可以的        System.out.println(s3.indexOf(97));        //第二个参数是指查找起点        System.out.println(s3.indexOf("21",7));        //lastIndexOf查找最后一个关键字所在位置        String s4 = "123321123";        System.out.println(s4.lastIndexOf("1"));        //replace 替换指定字符        String s5 = "a b c d     ";        String s6 = s5.replace(' ', '@');        System.out.println(s6);        //split分割        String s7 = "a|b,c d ef     ";        String arr[] = s7.split(" ");        for (String string : arr) {            System.out.println(string);        }        //charAt获取某个位置的字符        String s8 = "abcdefg";        System.out.println(s8.charAt(0));    }}

实例:检查是不是.java文件

public void java1(String s) {        String  string = "";        for (int i = s.lastIndexOf("."); i < s.length(); i++) {            string += s.charAt(i);        }        if (string.equals(".java")) {            System.out.println("您输入的是Java文件");        }else{            System.out.println("不是Java文件");        }    }    public static void main(String[] args) {        Scanner scanner  = new Scanner(System.in);        Test2 test  =  new Test2();        System.out.println("请输入您的文件名:");        String string = scanner.next();        test.java1(string);        }

实例:将字符串中的i改为1.O该问0

public String phone(String s) {        String s1 = s.replace("O", "0");        String s2 = s1.replace("i", "1");        return s2;    }    public static void main(String[] args) {        Scanner scanner  = new Scanner(System.in);        Test2 test  =  new Test2();        System.out.println("请输入手机充值卡密码:");        String string2 = scanner.next();        String string3 = test.phone(string2);        System.out.println(string3);    }}

实例:字符串My_English_NaMe改为myENGLISHNAME

public String daxiaoxie(String str) {        String[] arr = str.split("_");        String s1 = arr[0];        String s2 = arr[1];        String s3 = arr[2];        String string ="";        string += s1.toLowerCase();        string += s2.toUpperCase();        string += s3.toUpperCase();        return string;    }    public static void main(String[] args) {        System.out.println("字符串My_English_NaMe改为myENGLISHNAME:");        String string4 = "My_English_NaMe";        System.out.println(test.daxiaoxie(string4));    }

实例:找出字符串中数字.英文.空格和其他字符的数量

public void T1(String s) {        int num1 = 0;//这是英文的个数        int num2 = 0;//这是数字的个数        int num3 = 0;//这是空格的个数        int num4 = 0;//这是其他字符的个数        for (int i = 0; i < s.length(); i++) {            char key = s.charAt(i);            if (key >= 'A'&&key <= 'Z') {                num1 += 1;            }else if(key >= 'a'&&key <= 'z') {                num1 += 1;            }else if(key >= 48 && key <= 57) {                num2 += 1;            }else if(key == ' ') {                num3 += 1;            }else{                num4 += 1;            }        }        System.out.println("英文字母的数量为"+num1);        System.out.println("数字的数量为"+num2);        System.out.println("空格的数量为"+num3);        System.out.println("其他字符的数量为"+num4);    }    public static void main(String[] args) {        Test3 test3 = new Test3();        String string = "    abCD1234#$%&";        test3.T1(string);    }

实例:去掉字符串中间的空格但中间的空格不去掉

//这行代码可以完成System.out.println(s2.replace(s2.trim(),s2.trim().replace(" ", "")));

实例:回文串的判定

public void T5(String string) {        int length = string.length();        int number = 0;        if (length % 2 ==0) {            for (int i = 0; i < length; i++) {                if(string.charAt(i) == string.charAt((length)-i-1)){                    number +=1;                }else{                    break;                }            }            if (number == length) {                System.out.println("这是个回串文");            }else{                System.out.println("这不是个回串文");            }        }else{            for (int i = 0; i < (length-1)/2; i++) {                if(string.charAt(i) == string.charAt((length)-i-1)){                    number +=1;                }else{                    break;                }        }            if (number == (length-1)/2) {                System.out.println("这是个回串文");            }else{                System.out.println("这不是个回串文");            }    }}    public static void main(String[] args) {        Test5 test5 = new Test5();        test5.T5("abba");    }

实例:删除字符串中的某个字符

public static void main(String[] args) {        Scanner scanner = new Scanner(System.in);        System.out.println("字符串");        String string = scanner.next();        System.out.println("字符");        String string2 = scanner.next();        for (String string3 : string.split(string2)) {            System.out.print(string3);        }    }

实例:每个字符后面插入一个空格

public static void main(String[] args) {        String string = "abcd";        String string2 = "";        for (int i = 0; i < string.length(); i++) {            string2 += string.charAt(i)+" ";        }        System.out.println(string2);    }

实例:随机生成一个4位的验证码(包含英文大小写和数字)

public static void main(String[] args) {        Random random = new Random();        int m=0;        do{            int n = random.nextInt(123);            if (n <= 122&& n >= 97) {                System.out.print((char)n);                m++;                continue;            }else if(n <= 90&& n >= 65){                System.out.print((char)n);                m++;                continue;            }else if(n <=57&& n >= 48 ){                System.out.print((char)n);                m++;                continue;            }else{                continue;            }        }while(m<4);    }

实例:学生抽奖

public static void main(String[] args) {        ArrayList<String> students = new ArrayList<String>();        Random random = new Random();        students.add("古一");        students.add("林二");        students.add("张三");        students.add("李四");        students.add("王五");        students.add("赵六");        students.add("刘七");        students.add("胡八");        students.add("陈九");        students.add("王十");        students.add("古十");        students.add("林九");        students.add("张八");        students.add("李七");        students.add("王六");        students.add("赵五");        students.add("刘四");        students.add("胡三");        students.add("陈二");        students.add("王一");//      int length = students.size();        System.out.println("\n三等奖的同学是:");        for (int i = 0; i < 6; i++) {            int n = random.nextInt(20-i);            System.out.print(students.get(n)+"\t");            students.remove(students.get(n));        }        System.out.println("\n二等奖的同学是:");        for (int i = 0; i < 2; i++) {            int n = random.nextInt(14-i);            System.out.print(students.get(n)+"\t");            students.remove(students.get(n));        }        System.out.println("\n一等奖的同学是:");        for (int i = 0; i < 1; i++) {            int n = random.nextInt(12-i);            System.out.println(students.get(n));            students.remove(students.get(n));        }    }