字符串操作(字符数统计及字符串反转)

1.字符统计

package com.homework;

//统计字符串中相同字符出现的次数

public class StatisticString {
    
        public static void main(String[] args) {
            
        
    

    
        String str = "abcdeaaadfec53543543253@!#@!#$$@@!@#@!#!@3";
        Boolean flag; 
        int count;
        for (int i = 0; i < str.length(); i++)
        {
            flag = true;
            count=0;
            for (int k = 0; k < i; k++)
            {
                if (str.charAt(i) == str.charAt(k)) flag = false;
            }
            if (flag == true)
            {
                for (int j = 0; j < str.length(); j++)
                {
                    if (str.charAt(i) == str.charAt(j))
                    {
                        count++;
                    }
                }
                System.out.println(str.charAt(i) + "出现" + count + "次");
            }
        }
    }
}

2.字符串反转

package com.homework;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

//字符串反转，如I love java 将反转成  java love I. 
public class StringReverse {

    public void swap(char[] arr, int begin, int end) {
        while(begin < end) {
            char temp = arr[begin];
            arr[begin] = arr[end];
            arr[end] = temp;
            begin++;
            end--;
        }
    }
    
    public String swapWords(String str) {
        char[] arr = str.toCharArray();
        swap(arr, 0, arr.length - 1);
        int begin = 0;
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] == ' ') {
                swap(arr, begin, i - 1);
                begin = i + 1;
            }
        }

        return new String(arr);
    }
    
    public static void main(String[] args) {
        //缺点：one前要有空格，不然“one”将反转为“eno”
        
        String str = " one two three four five";
        System.out.println(new StringReverse().swapWords(str));
        
        
        //******************************************************
        //以上为全部程序，下面为补充
        
        //******************************************************
        //利用jdk自带方法实现以上功能
        
        //public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        String str1 = sc.nextLine();
        
        String[] sArr = str1.split(" ");//I love java
        
        List<String> list = new ArrayList<String>();
        
        list = Arrays.asList(sArr);
        
//        for(int i=0;i<sArr.length;i++){
//            list.add(sArr[i]);
//        }
        
        Collections.reverse(list);
        
        for(String word:list){
            System.out.print(word+" ");
        }
    //   }
        //结果同上
        //****************************************************************************
        
        
        //补充：
        //利用jdk自带方法将字符串反转（如将“abcd”反转为“dcba”）
        
        str="abxggsfd";
        System.out.println(new StringBuilder(str).reverse().toString());
    }
    
    // 结果为  dfsggxba
    
}

控制台输出

补充：你知道 “ 回 ” 字有四种写法吗？？？？？？？？？？？？？？？？？

               回、囘、囬、囗

   七种字符串反转方法

import java.util.Stack;
public class StringReverse {
  
 public static String reverse1(String s) {
  int length = s.length();
  if (length <= 1)
   return s;
  String left = s.substring(0, length / 2);
  String right = s.substring(length / 2, length);
  return reverse1(right) + reverse1(left);
 }
  
 public static String reverse2(String s) {
  int length = s.length();
  String reverse = "";
  for (int i = 0; i < length; i++)
   reverse = s.charAt(i) + reverse;
  return reverse;
 }
  
 public static String reverse3(String s) {
  char[] array = s.toCharArray();
  String reverse = "";
  for (int i = array.length - 1; i >= 0; i--)
   reverse += array[i];
  
  return reverse;
 }
  
 public static String reverse4(String s) {
  return new StringBuffer(s).reverse().toString();
 }
  
 public static String reverse5(String orig) {
  char[] s = orig.toCharArray();
  int n = s.length - 1;
  int halfLength = n / 2;
  for (int i = 0; i <= halfLength; i++) {
   char temp = s[i];
   s[i] = s[n - i];
   s[n - i] = temp;
  }
  return new String(s);
 }
  
 public static String reverse6(String s) {
  
  char[] str = s.toCharArray();
  
  int begin = 0;
  int end = s.length() - 1;
  
  while (begin < end) {
   str[begin] = (char) (str[begin] ^ str[end]);
   str[end] = (char) (str[begin] ^ str[end]);
   str[begin] = (char) (str[end] ^ str[begin]);
   begin++;
   end--;
  }
  
  return new String(str);
 }
  
 public static String reverse7(String s) {
  char[] str = s.toCharArray();
  Stack<Character> stack = new Stack<Character>();
  for (int i = 0; i < str.length; i++)
   stack.push(str[i]);
  
  String reversed = "";
  for (int i = 0; i < str.length; i++)
   reversed += stack.pop();
  
  return reversed;
 }
  
}