java_第二章 字符串

1.实现字符串的大小写字母的相互转换。

import java.util.Scanner;public class Day {public static void main(String[] args) {StringBuffer s1 = new StringBuffer();// String s2 = "abcDEF";Scanner sc = new Scanner(System.in);String s2 = sc.next();char c[] = s2.toCharArray();for (int i = 0; i < s2.length(); i++) {if (c[i] >= 97) {s1.append((c[i] + "").toUpperCase());}else {s1.append((c[i] + "").toLowerCase());}}System.out.println(s2);System.out.println(s1);}}/*LMwxyLMwxylmWXY*/

2.分析输入字符串中的单词，并输出其中单词的个数

import java.util.Scanner;public class Day {public static void main(String[] args) {int count = 0;String sentence = "I am W.X.Y,he is my boyfriend.LM?what's that?";Scanner s = new Scanner(sentence).useDelimiter(" |,|\\?|\\.");while (s.hasNext()) {count++;System.out.println(s.next());}System.out.println("这段短文单词的个数是：" + count);}}/*IamWXYheismyboyfriendLMwhat'sthat这段短文单词的个数是：12*/

3.将字符串“.ymene tsrow sih si nam yrevE”反转。

public class Day {public String convert(String s) {String ans = "";if (s == null && s.length() == 0)return ans;for (int i = s.length() - 1; i >= 0; i--) {ans += s.charAt(i);}return ans;}public static void main(String[] args) {Day aa = new Day();String ans = aa.convert(".ymene tsrow sih si nam yrevE");System.out.println(ans);}}/* * Every man is his worst enemy. */

4.实现输入一个字符串，打印出其中所有的数字

public class Day {public static void main(String[] args) {String str = "w11x12ylm22";str = str.trim();String str2 = "";if (str != null && !"".equals(str)) {for (int i = 0; i < str.length(); i++) {if (str.charAt(i) >= 48 && str.charAt(i) <= 57) {str2 += str.charAt(i);}}}System.out.println(str2);}}/*111222*/

import java.util.Scanner;public class Day {public static void main(String args[]) {System.out.println("输入一个字符串:");Scanner sc = new Scanner(System.in);String str = sc.next();StringBuffer str1 = new StringBuffer();char[] a = str.toCharArray();for (int i = 0; i < a.length; i++) {if (Character.isDigit(a[i])) {// 判断是否为包含数字str1.append(a[i]);}}System.out.println(str1);}}/*输入一个字符串:w1y1xxlm2112*/