BlueJ Jave 新手问题

[qq_31739799]

大家好，我最近刚刚开始学习编程。 今天有个作业是让我们做一个类似于超速罚单的程序。 但是我怎么都显示不出来罚单。


/**
* Lab3b for secction 3
*
* @author (Castiel)
* @version (01-10-2015)
*/
public class Driver
{
// instance variables - replace the example below with your own
private String name;
private String driverLicense;
private int speedInKmPerHour;
private String driverStanding;

/**
* Default Constructor for objects of class Driver
*/
public Driver()
{
// initialise instance variables
name = "";
driverLicense = "";
speedInKmPerHour = 0;
driverStanding = "";
}

/**
* non defaul constructor should validate the parameter as follows:
*
* name and driverLicense can not be null, if the passed parameter was null, an empty string " " will be assogned to the instance variable
*
* validates the speed parameter and uses it if it is positive; otherwise speed will be set to 0
*
* driverStanding will be set to an empty string
*
* @param driverName
* @param licenseNumber
* @param speed
* @param standing
*/
public Driver(String driverName, String licenseNumber, int speed, String standing)
{
if (driverName != null){
name = driverName;
}
else{
name = "";
}

if (licenseNumber != null){
driverLicense = licenseNumber;
}
else{
driverLicense = "";
}

if (speed >=0 ){
speedInKmPerHour = speed;
}
else{
speedInKmPerHour = 0;
}

driverStanding = "";
}

// accessor methods
/**
* method getName
*
* @return drivers name
*/
public String getName(){
return name;
}

/**
* method getdriverLicense
*
* @return drivers License
*/
public String getDriverLicense(){
return driverLicense;
}

/**
* method getSpeedInKmPerHour
*
* @return speed
*/
public int getSpeedInKmPerHour(){
return speedInKmPerHour;
}

/**
* method getDriverStanding
*
* @return driver Standing
*/
public String getDriverStanding(){
return driverStanding;
}

//mutator methods
/**
* mutator method of name
* @param driverName as String
*/
public void setName(String driverName){
if(driverName != null){
name = driverName;
}
else{
name = "";
}
}

/**
* mutator method of driverLicense
* @param licenseNumber as String
*/
public void setDriverLicense(String licenseNumber){
if(licenseNumber != null){
driverLicense = licenseNumber;
}
else{
driverLicense = "";
}
}

/**
* mutator method of speedInKmPerHour
* @param speed as int
*/
public void setSpeedInKmPerHour(int speed){
if(speed >= 0){
speedInKmPerHour = speed;
}
else{System.out.println("invalid input speed cannot benegative");
}
if(speedInKmPerHour <= 60){
driverStanding = "no ticket";
}
if(speedInKmPerHour > 60){
if(speedInKmPerHour <=80){
driverStanding = "small ticket";
}
}
if(speedInKmPerHour > 80){
driverStanding = "big ticket";
}
}

/**
* method drivers detail
*/
public void driverdetail(){
System.out.println("Driver name:" + " " +name);
System.out.println("Driver License::" + " " +driverLicense);
System.out.println("Speed:" + " " + speedInKmPerHour + "K/H");
System.out.println("Driver Standing:" + driverStanding);
}
}




上面是我写的代码
driverDetail
应该长这样
Driver name: John James
Driver License: 123456
Speed: 70 K/H
Driver Standing: small ticket


但是我出来的都是这样
Driver name: John James
Driver License:: 123456
Speed: 70K/H
Driver Standing: null

[oh_Maxy]

public Driver(String driverName, String licenseNumber, int speed, String standing) 这个构造方法的入参standing没有赋值给属性driverStanding 增加一句： driverStanding=standing; 就可以了。

[qq_31739799]

driverStanding = ""; 改成driverStandin=standing; 之后还是不行啊。 Create object的时候问我要String standing 的value。 我只好用“” 然后出来的是 Driver name: John James Driver License:: 123456 Speed: 70K/H Driver Standing: 求解－ － 谢谢