java中String类中API的实现

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java String 类方法的再实现

/***@author StormMaybin*@Date 2016-05-20*/

java String 类中 trim 方法的实现：

class Function{    /**    *实现字符串反转功能    *@param String str    *@return str    */    public static String reverseString(String str)    {        //1、字符串变数组        char [] chs = str.toCharArray();        //2、反转数组        reverse(chs);        //3、将数组变成字符串        return new String (chs);    }    /**    *实现字符串反转功能（重载）    *@param String str,int start,int end    *@return String    */    public static String reverseString(String str, int start, int end)    {        char [] chs = str.toCharArray();        reverse(chs,start,end);        return new String(chs);    }    /**    *实现字符数组反转功能    *@param char[]str    *@return void    */    private static void reverse (char [] str)    {        for (int start = 0, end = str.length - 1; start <= end; start++, end--)        {            swap (str, start, end);        }    }    /**    *实现字符数组反转功能（重载）    *@param char[] str,int start,int end    *@return void    */    private static void reverse (char [] str, int start, int end)    {        for (end--;start <= end; start++, end--)        {            swap(str, start, end);        }    }    /**    *实现数组元素交换功能    *@param char[]str,int a,int b    *@return void    */    private static void swap (char [] str, int a, int b)    {        char temp = str[a];        str[a] = str[b];        str[b] = temp;    }}/***测试类*/public class ReverseString {    public static void main (String [] arguments)    {        String str = "abcdefg";        String storm = Function.reverseString(str);        String StormMaybin = Function.reverseString(str,0,4);        System.out.println (storm);        System.out.println(StormMaybin);    }}

用 java 实现求一个字符串中子串出现的次数：

class Function{    /**    *@方法功能：计算一个字符串里面子串出现的次数    *@param String str1, String str2    *@return int    */    public static int subStringCount_1(String str1, String str2)    {        int count = 0;        int index = 0;        while ((index = str1.indexOf(str2)) != -1)        {            count++;            str1 = str1.substring (index + str2.length());        }        return count;    }    /**    *@计算子串在字符串出现的次数方法2    *@param String str1, str2    *@return int    */    public static int subStringCount_2(String str1, String str2)    {        int count = 0;        int index = 0;        while ((index = (str1.indexOf(str2,index))) != -1)        {            index += str2.length();            count ++;        }        return count;    }}/***测试类*/public class SubStringCount{    public static void main (String [] arguments)    {        String str = "abcdabcdabcdabcdhdsjdabcd";        int count = Function.subStringCount_2(str,"abcd");        System.out.println (count);    }}

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