java判断索引

package com.hanqi;
import java.util.*;
public class zuoyequsuoyin {
    public static void main(String[] args)
    {
        String a = "abcdefghijklmnopqrstuvwxyz";
        
        int b = (a.length());
        
        if(a.indexOf("abc")==0)
        {
            System.out.println("判断开始的索引"+a.startsWith("abc")); 
        }
        else
        {
            System.out.println("您的输入有误，请在条件里从新定义条件");
        }
        
        if(a.indexOf("yz")== b-2)
        {
                
                System.out.println("判断结束的索引"+a.endsWith("yz")); 
        }
        else
        {
            System.out.println("您的输入有误，请在条件里从新定义条件");
        }
        
        
        
            
    }

}