我的节目是：
public class Vehicle {
String colors[] = {"Red", "White", "Blue", "black", "Silver"};
private String name;
private String model;
double cost_price;
int year;
int quantity;
double selling_price;
String registration_no;
Vehicle(String name, String model, int year, double cost_price) {
this.name = name;
this.model = model;
this.year = year;
this.cost_price = cost_price;
this.quantity = 0;
this.selling_price = 0;
}
Vehicle(String name, String model, int quantity, double cost_price, String registration_no) {
this.name = name;
this.model = model;
this.quantity = quantity;
this.cost_price = cost_price;
this.selling_price = cost_price;
this.registration_no = registration_no;
}
public void setname(String name) {
this.name = name;
}
public void setmodel(String model) {
this.model = model;
}
public String getname() {
return name;
}
public String getmodel() {
return model;
}
public double calSellingPrice(int markup) {
return cost_price + ((cost_price * markup) / 100);
}
public int updateQuantity(int amount) {
return quantity;
}
public String tostring() {
}
/**
* @param args the command line arguments
*/
}
class Vehicletest {
public static void main(String[] args) {
// TODO code application logic here
Vehicle v1 = new Vehicle("Ferrari", "Enzo", 2011, 250000);
v1 = new Vehicle("Ferrari", "Enzo", 6, 250000, "PK07LVD");
Vehicle v2 = new Vehicle("Audi", "R8", 2008, 550000);
v2 = new Vehicle("Audi", "R8", 9, 550000, "ADDY104");
Vehicle v3 = new Vehicle("RangeRover", "Evoque", 2010, 578000);
v3 = new Vehicle("RangeRover", "Evoque", 3, 578000, "OHZ2692");
Vehicle v4 = new Vehicle("Lamborghine", "Aventador", 2013, 980000);
v4 = new Vehicle("Lamborghine", "Aventador", 5, 980000, "BB03813");
Vehicle v5 = new Vehicle("Porsche", "Carrera", 2006, 675000);
v5 = new Vehicle("Porsche", "Carrera", 15, 675000, "BD51SMR");
ArrayList uwiMotors = new ArrayList();
uwiMotors.add(v1);
uwiMotors.add(v2);
uwiMotors.add(v3);
uwiMotors.add(v4);
uwiMotors.add(v5);
System.out.println(v1.colors);
System.out.println(v1.cost_price);
System.out.println(v1.quantity);
System.out.println(v1.registration_no);
System.out.println(v1.selling_price);
System.out.println(v1.year);
for (int i = 0; i < uwiMotors.size(); i++) {
System.out.println(uwiMotors.get(i));
}
}
}
我做错了吗？
我对两个构造函数感到困惑。因为如果我将引用变量初始化为两个构造函数，那么值是否会被更改？如何从Arraylist输出值？
我是否必须覆盖toString()方法？如果是，那我该怎么做？
答案 0 :(得分：1)
您的代码中存在多个问题。首先，您应该阅读constructors。你只得到控制台上的哈希，因为你告诉Java输出一个对象。由于您的对象没有正确的toString方法，因此无法知道输出的外观。
三个提示：
Vehicle(String name, String model, int year, double cost_price) {
//as you have it above
}
//add year to this constructor
Vehicle(String name, String model, int year, int quantity, double cost_price, String registration_no) {
this(name, model, year, cost_price);
this.quantity = quantity;
this.selling_price = cost_price;
this.registration_no = registration_no;
}
和
@Override
public String toString() { //camelCase is important!
return this.name + ", " + this.model; //adopt this part as you want it to
}
最后：
//Vehicle v1 = new Vehicle("Ferrari", "Enzo", 2011, 250000);
//you cannot call two different constructors
Vehicle v1 = new Vehicle("Ferrari", "Enzo", 2011, 6, 250000, "PK07LVD");
答案 1 :(得分：1)
我对两个构造函数感到困惑。因为如果我将引用变量初始化为两个构造函数，则不会更改值吗？
是的，实际上您正在用新的对象替换第一个对象，因此v1-v5的初始化可以简化为以下内容：
Vehicle v1;
v1 = new Vehicle("Ferrari", "Enzo", 6, 250000, "PK07LVD");
Vehicle v2;
v2 = new Vehicle("Audi", "R8", 9, 550000, "ADDY104");
Vehicle v3;
v3 = new Vehicle("RangeRover", "Evoque", 3, 578000, "OHZ2692");
Vehicle v4;
v4 = new Vehicle("Lamborghine", "Aventador", 5, 980000, "BB03813");
Vehicle v5;
v5 = new Vehicle("Porsche", "Carrera", 15, 675000, "BD51SMR");
你应该写一个新的构造函数，你可以在其中传递初始化所需的所有参数，或者使用其中一个构造函数，然后使用setter来处理剩下的内容。
如何从Arraylist输出值？我是否必须覆盖toString（）方法？如果是，那我该怎么做？
有很多方法可以解决这个问题。覆盖toString将是最简单的。以下是你将如何做到这一点：
public String tostring() {
return "name=" + this.name + ", model=" + this.model + ", cost_price=" + this.cost_price + ", year=" + this.year + ", quantity=" + this.quantity + selling_price=" + this.selling_price+ ", registration=" + registration;
}
随意修改此选项以仅包含您需要的字段。
然后你可以通过你的arraylist循环来编写它，这样System.out就像这样：
for (Vehicles v : uwiMotors)
{
System.out.println(v);
}
答案 2 :(得分：1)
你的代码会给你一个'哈希'列表（它实际上不是哈希码），因为这是toString的默认实现。
代码的基本布局应该是这样的（我删除了一些字段以保持长度，并使用Apache commons-lang来帮助equals，hashCode和toString方法）：
public class Vehicle
{
private String name;
private String model;
private String registration;
public Vehicle(String name, String model)
{
this.name = name;
this.model = model;
}
public Vehicle(String name, String model, String registration)
{
this(name, model);
this.registration = registration;
}
public String getName()
{
return name;
}
public String getModel()
{
return model;
}
public String getRegistration()
{
return registration;
}
public String getRegistration()
{
return registration;
}
@Override
public boolean equals(Object obj)
{
return this == obj || obj instanceof Vehicle &&
new EqualsBuilder()
.append(getName(), ((Vehicle)obj).getName())
.append(getModel(), ((Vehicle)obj).getModel())
.append(getRegistration(), ((Vehicle)obj).getRegistration())
.isEquals();
}
@Override
public int hashCode()
{
return new HashCodeBuilder()
.append(getName())
.append(getModel())
.append(getRegistration())
.toHashCode();
}
@Override
public String toString()
{
return new ToStringBuilder(this, ToStringStyle.MULTI_LINE_STYLE)
.append("name", getName())
.append("model", getModel())
.append("registration", getRegistration())
.toString();
}
}
答案 3 :(得分：0)
暂时让我们忽略代码中的错误编码做法。我希望以下代码是您正在寻找的？
for (int i = 0; i < uwiMotors.size(); i++) {
Vehicle vehicle = (Vehicle)uwiMotors.get(i);
// System.out.println(vehicle.cost_price+","+vehicle.quantity);
System.out.println(vehicle);// If vehicle object overrides the toString method
}
答案 4 :(得分：0)
是的，两个构造函数将更改变量的值，只是因为您只是创建新对象并将其分配给变量。正如@ Christian Kullmann所写的你应该考虑使用'this（arg goes here）'来调用另一个构造函数。
打印Arraylist元素您只需循环迭代它们并逐个打印（如您所做）。但是在覆盖toString的情况下你只需像这样写
public String toString(){
return "some text";
}