我正在制作一个有超级（船）和两个子类（SailBoat，Powerboat）的船只计划，我必须打印出所有的船只信息和价格，以及最昂贵的船只和它的信息。这是我遇到麻烦的部分，因为我不完全确定如何去做。这是我到目前为止所拥有的......
船类：
public class Boat {
String color;
int length;
public Boat() {
color = "white";
length = 20;
}
public Boat(String col, int leng) {
color = col;
length = leng;
}
public boolean setColor(String col) {
if ("white".equals(col) || "red".equals(col) || "blue".equals(col) || "yellow".equals(col)) {
col = color;
return true;
} else {
System.out.println("Error: can only be white, red, blue or yellow");
return false;
}
}
public String getColor() {
return color;
}
public boolean setLength(int leng) {
if (leng < 20 || leng > 50) {
leng = length;
System.out.println("Sail Boats can only be between 20 and 50 feet, inclusively.");
return false;
} else {
return true;
}
}
public int getLength() {
return length;
}
public String toString() {
String string;
string = String.format("Color = " + color + " Length = " + length);
return string;
}
public int calcPrice() {
int price;
price = 5000 + length;
return price;
}
}
PowerBoat Subclass
import java.text.NumberFormat;
public class PowerBoat extends Boat {
int engineSize;
public PowerBoat() {
super();
engineSize = 5;
}
public PowerBoat(String col, int len, int esize) {
this.color = col;
this.length = len;
engineSize = esize;
}
public boolean setEngineSize(int esize) {
if (esize < 5 || esize > 350) {
System.out.println(
"Error: That engine is too powerful. The engine size must be between 1 and 350, inclusively");
esize = engineSize;
return false;
} else {
return true;
}
}
public int calcPrice() {
int price;
price = 5000 + length * 300 + engineSize * 20;
return price;
}
public String toString() {
NumberFormat nf = NumberFormat.getCurrencyInstance();
nf.setMinimumFractionDigits(2);
nf.setMaximumFractionDigits(2);
return super.toString() + " Engine Size = " + engineSize + " Price = " + nf.format(calcPrice());
}
}
SailBoat子类
import java.text.NumberFormat;
public class SailBoat extends Boat {
int numSails;
public SailBoat() {
numSails = 0;
}
public SailBoat(String col, int leng, int numsail) {
color = col;
length = leng;
numSails = numsail;
}
public boolean setNumSails(int nsails) {
if (nsails < 1 || nsails > 4) {
nsails = numSails;
return false;
} else {
return true;
}
} // end setNumSails
public int getNumSails() {
return numSails;
}
public int calcPrice() {
int price;
price = length * 1000 + numSails * 2000;
return price;
}
public String toString() {
NumberFormat nf = NumberFormat.getCurrencyInstance();
nf.setMinimumFractionDigits(2);
nf.setMaximumFractionDigits(2);
return super.toString() + "Color: " + color + " Length: " + length + " Number Sails = " + numSails + " Cost = "
+ nf.format(calcPrice());
}
public int getTotalCost() {
int totalCost = 0;
totalCost += calcPrice();
return totalCost;
}
}
库存类（测试人员）
import java.util.ArrayList;
public class Inventory {
public static void main(String[] args) {
// boat objects
Boat pb1 = new PowerBoat("blue", 22, 60);
Boat sb1 = new SailBoat("white", 20, 1);
Boat sb2 = new SailBoat("red", 42, 3);
Boat pb2 = new PowerBoat("yellow", 35, 80);
Boat pb3 = new PowerBoat("red", 50, 120);
Boat sb3 = new SailBoat("blue", 33, 2);
Boat pb4 = new PowerBoat("white", 20, 10);
ArrayList<Boat> AL = new ArrayList<Boat>();
// add boat objects to arraylist
AL.add(pb1);
AL.add(sb1);
AL.add(sb2);
AL.add(pb2);
AL.add(pb3);
AL.add(sb3);
AL.add(pb4);
// print all boat objects
System.out.println("Print all boats");
for (Boat anyBoat : AL) {
System.out.println(anyBoat.toString());
}
int max = 0;
int totalcost = 0;
Boat mostExpensiveBoat = null;
for (Boat anyBoat : AL) {
if (anyBoat instanceof SailBoat) {
totalcost += anyBoat.calcPrice();
if (anyBoat.calcPrice() > max) {
max = anyBoat.calcPrice();
mostExpensiveBoat = anyBoat;
}
}
}
}
}
我真的很困惑如何完成这个程序，我打算在打印完所有船信息后得到的结果是这个..
Total price of all boats is $ 170,500.00
Most Expensive Boat: Color = red Length = 42 Number Sails = 3 Cost = $ 48,000.00
任何帮助将不胜感激。谢谢。
答案 0 :(得分：2)
您应该纠正一些设计缺陷：
Boat课程应为interface或abstract。你不能拥有一艘不是动力艇或帆船的船，所以你不应该实例化它。private。Boat的子类定义的方法摘要（例如calcPrice）。如果你能够使用Java 8，那么有一个很好的方法来获得最昂贵的船。以下代码将打印最昂贵的船（使用Boat.toString），如果有的话。
allBoats.stream()
.max(Comparator.comparingInt(Boat::calcPrince))
.ifPresent(System.out::println);
这避免了必须编写手动迭代列表比较价格的代码。它还应对空列表的情况（这意味着没有最大值）。否则，您需要在打印前初始化为null并与null进行比较。
答案 1 :(得分：0)
你的for循环应如下所示：
for (Boat anyBoat : AL) {
totalcost += anyBoat.calcPrice();
if (anyBoat.calcPrice() > max) {
max = anyBoat.calcPrice();
mostExpensiveBoat = anyBoat;
}
}
如果它是一个帆船并不重要，你只想打印最昂贵的信息，这样你就可以删除条件的实例。之后：
NumberFormat nf = NumberFormat.getCurrencyInstance();
nf.setMinimumFractionDigits(2);
nf.setMaximumFractionDigits(2);
System.out.println("Total price of all boats is " + nf.format(totalcost));
System.out.println("Most expensive boat: " + mostExpensiveBoat.toString());
应该可以工作，因为你已经覆盖了toString（）方法。
还有一件事：在你的SailBoat toString（）方法中，你正在做：
return super.toString() + "Color: " + color + " Length: " + length + " Number Sails = " + numSails + " Cost = "
+ nf.format(calcPrice());
当你调用super.toString（）时，你打印的颜色和长度是两次;只需致电
return super.toString() + " Number Sails = " + numSails + " Cost = " + nf.format(calcPrice());