Isn't this valid?? I need to throw an exception if the second character is not in uppercase

public class TeacherAssistant {

  public static String validatedFieldName(String fieldName) {
    // These things should be verified:
    // 1.  Member fields must start with an 'm'
    // 2.  The second letter in the field name must be uppercased to ensure camel-casing
    // NOTE:  To check if something is not equal use the != symbol. eg: 3 != 4
    if(fieldName.indexOf(0)!='m'){
      throw new IllegalArgumentException("The first letter must be m");
    }
    if(isLowerCase(fieldName.charAt(1)))
      throw new IllegalArgumentException("Following m must be a Upper Case Letter");
    return fieldName;
  }

}