28. string类中方法练习

1. 自己写trim方法

public class Demo3 {
    public static void main(String[] args) {
        System.out.println(myTrim("     123     "));
    }
    //需求：去除字符串两边空格的函数
    public static String myTrim(String str){
        int start = 0;
        int end = str.length()-1;
        //去掉前面的空格
        for (int i = 0; i < str.length()-1; i++) {
            char ch = str.charAt(start);
            if(ch == ' '){
                start++;
            }else{
                break;
            }
        }
        //去掉后面的空格

        for (int i = end; i >0; i--) {
            char ch = str.charAt(i);
            if(ch == ' '){
                end--;
            }else{
                break;
            }
        }
        //截取字符串(因为不包含最后一位数，所以加1)
        return str.substring(start,end+1);

    }
}

2.获取上传文件名  "D:\\20120512\\day12\\Demo1.java"

public class Demo4 {
    public static void main(String[] args) {
        System.out.println(getFilename("D:\\20120512\\day12\\Demo1.java"));
    }

    //需求：获取上传文件名  "D:\\20120512\\day12\\Demo1.java"
    public static String getFilename(String path){

        //根据\获取最后一个的索引+1
        int start = path.lastIndexOf('\\')+1;

        return path.substring(start);
    }
}

3.将字符串对象中存储的字符反序

public class Demo5 {
    public static void main(String[] args) {
        System.out.println(reaverseString("hello"));
    }

    //需求：将字符串对象中存储的字符反序
    public static String reaverseString(String str){
        char[] ch = str.toCharArray();
        for (int start = 0,end = ch.length-1; start < end; start++,end--) {
            char temp = ch[start];
            ch[start] = ch[end];
            ch[end] = temp;
        }
        return new String(ch);
    }
}

4. 求一个子串在整串中出现的次数

public class Demo6 {
    public static void main(String[] args) {
        System.out.println(getCount("abcabcjgejgabc","abc"));
    }
    //求一个子串在整串中出现的次数
    public static int getCount( String src , String tag ){
          // 0. 定义索引变量和统计个数的变量
          int index = 0;
          int count = 0;
          // 1. 写循环判断
          while ( ( index = src.indexOf(tag) ) != -1 ){
              src = src.substring( index + tag.length() );   // index 4 + 4 = 8
              count++;
          }
          return count;
    }
}