菜鸟求救！大侠们帮忙解决一下吧

Question

 import   java.io.*; 
public  class bb 
{ 
       public static void main(String [] args) throws Exception 
       { 
          int x=c; 
          byte[] br = new byte[100]; 
          System.out.println("请输入一串字符：") 
          InputStream is = System.in; 
              InputStreamReader isr=new InputStreamReader(is); 
              BufferedReader br=new BufferedReader(isr); 
              String str=br.readLine(); 
              char[] ch=new char[str.length()]; 
              str.getChars(0, str.length(), ch, 0); 
              for(int a=0;a<str.length();a++) 
               { 
                if (str==null) 
                { 
            throw   new   IllegalArgumentException("参数数组c为空"); 
            System.exit(0);    
                } 
              if(str[a]=x)  
                { 
               System.out.println(a); 
                } 
              else 
                { 
               System.out.println("-1"); 
                }  
              
               } 
       } 
} 
错误  
--------------------Configuration: <Default>-------------------- 
G:\java\lesson1\bb.java:9: ';' expected 
              InputStream is = System.in; 
                  ^ 
1 error Process completed.  
 

Answer 1

int x=c; 
          byte[] br = new byte[100]; 
          System.out.println("请输入一串字符：");
          InputStream is = System.in; 
仅仅是改了这个错误 能不能正常运行你先试试再说

Answer 2

import   java.io.*; import java.io.BufferedReader;
public  class bb 
{ 
       public static void main(String [] args) throws Exception 
       { 
              char  x='c';
            
              
           
              System.out.println("请输入一串字符：") ;
              InputStream is = System.in; 
              InputStreamReader isr=new InputStreamReader(is); 
              BufferedReader br=new BufferedReader(isr); 
              String str=br.readLine(); 
             // char[] ch=new char[str.length()]; 
              //str.getChars(0, str.length(), ch, 0); 
              for(int a=0;a<str.length();a++) 
               { 
                if (str==null) 
                {
                  System.exit(0);    
                  } 
                
                
               if(str.charAt(a)==x)  
                { 
                   System.out.println(a); 
                } 
                else 
                { 
                   System.out.println("-1"); 
                   
                }  
              
               } 
       } 
} 
可以了
只是 if(str.charAt(a)==x)  是单个字母比较的 怎样让他从一个字符串里逐个比较