help with exercise needed

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("Member fields must start with an 'm'");
    }
    if(!Character.isUpperCase(fieldName.indexOf(1))){
      throw new IllegalArgumentException("second letter must be uppercased!");
    }

    return fieldName;
  }

}