java_String类练习

 public class StringTest {
     //1.模拟trim方法，去除字符串两端的空格
     public static void main(String[] args) {
         String str = "  ai  kang        ";
         char c = str.charAt(0);
        while (true){
            if(str.startsWith(" ")){
                str = str.substring(1);
            }else if(str.endsWith(" ")){
                str = str.substring(0,str.length()-1);
            }else{
                break;
            }
        }
         System.out.println(str);
     }
 }

public class StringTest01 {
    //2.将一个字符串进行反转，将字符串中指定部分进行反转，比如"abcdefg"反转
    public static void main(String[] args) {
        String str = "abcdefg";
        StringTest01 stringTest01 = new StringTest01();
        String s = stringTest01.StringDemo01(str, 1);
        System.out.println(s);
        String s1 = stringTest01.StringDemo02(str, 1);
        System.out.println(s1);

    }

    //方法一
    public String StringDemo01(String string,int start){
        String str =string;
        char[] c = str.toCharArray();
        for (int i = start; i < str.length()/2; i++) {
            char c1 = c[c.length-i-1];
            c[c.length-i-1] = c[i];
            c[i] = c1;
        }
        return new String(c);
    }

    //方法二
    public String StringDemo02(String string,int start){
        StringBuilder str = new StringBuilder(string.length());
        char[] c = string.toCharArray();
        str.append(string.substring(0,start));
        for(int j = string.length()-1-start;j>=start;j--){
            str.append(c[j]);
        }
        str.append(string.substring(string.length()-start));
        return new String(str);
    }

}

 public class StringTest02 {
     //3.获取一个字符串在另一个字符串中出现的次数如"ab"在"abkkcadkabkebfabkskab"中出现的次数
     public static void main(String[] args) {
         String str = "abkkcadkabkebfabkskab";
         String indexstr = "ab";
         StringTest02 stringTest02 = new StringTest02();
         int i = stringTest02.indexNum(str, indexstr);
         System.out.println(i);

     }
    public int indexNum(String str,String indexstr){
        int num = 0;
        for(;;){
            int i = str.indexOf(indexstr);
            if(i != -1){
                str = str.substring(i+indexstr.length());
                num++;
            }else{
                return num;
            }
        }

    }
 }