toString()重写

public String toString(){

Class<?> key = this.getClass();
Field[] fields = key.getDeclaredFields();
StringBuffer sb = new StringBuffer();
try{
    for(Field field : fields){
        sb = sb.append(field.getName()).append("=").append(field.get(this)).append(" ");
    }
}catch(Exception e){
    e.printStackTrace();
}
return sb.toString();

}