java 产生随机码

public class Test {

    private char[] c;
  public  Test() {
   Strings="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
     c = s.toCharArray();
    }
    publicString getValidateCode() {
     inti1 = (int)(Math.random()*c.length);
     inti2 = (int)(Math.random()*c.length);
     inti3 = (int)(Math.random()*c.length);
     inti4 = (int)(Math.random()*c.length);
     
     return""+c[i1]+c[i2]+c[i3]+c[i4];
    }
    
    publicstatic void main(String[] args) {
     Testa = new Test();
     for(inti=1;i<100;i++)
     {
      
     System.out.print(a.getValidateCode()+"\t");
        if(i==0)
        {
         System.out.println();
        }
     }
    }
  

}