我正在开发一个java类的项目，但我陷入了这个问题。当我运行程序并测试菜单选项 4 和 5 时，我得到要打印的列表，但它们打印为 [Dog@42a57993, Dog@75b84c92, Dog@6bc7c054]，而不是打印数组中的实际信息。
import java.util.ArrayList;
import java.util.Scanner;
public class Driver {
private static ArrayList<Dog> dogList = new ArrayList<Dog>();
private static ArrayList<Monkey> monkeyList = new ArrayList<Monkey>();
public static void main(String[] args) {
initializeDogList();
initializeMonkeyList();
Scanner input = new Scanner(System.in); // scanner class object
char option;
do // loop until user quits program
{
displayMenu();
option = input.next().charAt(0);
if (option == '1') { // intakeNewDog method is called
intakeNewDog(input);
}
else if (option == '2') { // intakeNewMonkey method is called
intakeNewMonkey(input);
}
else if (option == '3') { // reserveAnimal method is called
reserveAnimal(input);
}
else if (option == '4') { // printAnimals method is called to print the dog list
printAnimals(option);
}
else if (option == '5') { // printAnimals method is called to print the monkey list
printAnimals(option);
}
else if (option == '6') { // printAnimals method is called to print all available animals
printAnimals(option);
}
else if (option == 'q') { // exit message prints and application stops running
System.out.print("You have exited the application.");
break;
}
else { // in the event of an invalid input, tells user and prompts for a new input
System.out.print("You have entered an invalid input. Please enter a valid input.");
}
}
while (option != 'q');
}
// This method prints the menu options
public static void displayMenu() {
System.out.println("\n\n");
System.out.println("\t\t\t\tRescue Animal System Menu");
System.out.println("[1] Intake a new dog");
System.out.println("[2] Intake a new monkey");
System.out.println("[3] Reserve an animal");
System.out.println("[4] Print a list of all dogs");
System.out.println("[5] Print a list of all monkeys");
System.out.println("[6] Print a list of all animals that are not reserved");
System.out.println("[q] Quit application");
System.out.println();
System.out.println("Enter a menu selection");
}
// Adds dogs to a list for testing
public static void initializeDogList() {
Dog dog1 = new Dog("Spot", "German Shepherd", "male", "1", "25.6", "05-12-2019", "United States", "intake", false, "United States");
Dog dog2 = new Dog("Rex", "Great Dane", "male", "3", "35.2", "02-03-2020", "United States", "Phase I", false, "United States");
Dog dog3 = new Dog("Bella", "Chihuahua", "female", "4", "25.6", "12-12-2019", "Canada", "in service", true, "Canada");
dogList.add(dog1);
dogList.add(dog2);
dogList.add(dog3);
}
// Adds monkeys to a list for testing
//Optional for testing
public static void initializeMonkeyList() {
Monkey monkey1 = new Monkey("Joe", "male", "2", "6.5", "04-18-2021", "United States", "in service", false, "United States", "Spider Monkey", "16.6", "16.4", "19.0");
Monkey monkey2 = new Monkey("Bob", "male", "3", "8.5", "07-20-2020", "Brazil", "Phase 4", true, "United States", "Capuchin", "19", "19.4", "15.5");
Monkey monkey3 = new Monkey("Lisa", "female", "1", "20.0", "07-07-2022", "Nairobi", "in service", true, "Nairobi", "Howler Monkry", "25.2", "14", "13.4");
monkeyList.add(monkey1);
monkeyList.add(monkey2);
monkeyList.add(monkey3);
}
// Complete the intakeNewDog method
// The input validation to check that the dog is not already in the list
// is done for you
public static void intakeNewDog(Scanner scanner) {
System.out.println("What is the dog's name?");
String name = scanner.nextLine();
for(Dog dog: dogList) {
if(dog.getName().equalsIgnoreCase(name)) {
System.out.println("\n\nThis dog is already in our system\n\n");
return; //returns to menu
}
}
System.out.println("What is the dog's breed?"); // this code is for adding a new dog
String breed = scanner.nextLine();
System.out.println("What is the dog's gender?");
String gender = scanner.nextLine();
System.out.println("What is the dog's age?");
String age = scanner.nextLine();
System.out.println("What is the dog's weight?");
String weight = scanner.nextLine();
System.out.println("What is the dog's acquisition date?");
String acquisitionDate = scanner.nextLine();
System.out.println("What is the dog's acquisition country?");
String acquisitionCountry = scanner.nextLine();
System.out.println("What is the dog's training status?");
String trainingStatus = scanner.nextLine();
System.out.println("Is this dog reserved?");
boolean reserved = scanner.nextBoolean();
scanner.nextLine();
System.out.println("Which country is the dog in service?");
String inServiceCountry = scanner.nextLine();
Dog dog4 = new Dog(name, breed, gender, age, weight, acquisitionDate, acquisitionCountry, trainingStatus, reserved, inServiceCountry);
dogList.add(dog4);
System.out.println("Your entry has been added to the Dog List.");
}
public static void intakeNewMonkey(Scanner scanner) {
System.out.println("What is the monkey's name?");
String name = scanner.nextLine();
for(Monkey monkey: monkeyList) {
if(monkey.getName().equalsIgnoreCase(name)) {
System.out.println("\n\nThis monkey is already in our system\n\n");
return;
}
}
System.out.println("What is the monkey's gender?"); // the following is to add a new monkey to the system
String gender = scanner.nextLine();
System.out.println("What is the monkey's age?");
String age = scanner.nextLine();
System.out.println("What is the monkey's weight?");
String weight = scanner.nextLine();
System.out.println("What is the monkey's acquisition date?");
String acquisitionDate = scanner.nextLine();
System.out.println("What is the monkey's acquisition country?");
String acquisitionCountry = scanner.nextLine();
System.out.println("What is the monkey's training status?");
String trainingStatus = scanner.nextLine();
System.out.println("Is this monkey reserved?");
boolean reserved = scanner.nextBoolean();
System.out.println("Which country is the monkey in service?");
String inServiceCountry = scanner.nextLine();
System.out.println("What is the monkey's species?");
String species = scanner.nextLine();
System.out.println("What is the tail length?");
String tailLength = scanner.nextLine();
System.out.println("What is the height?");
String height = scanner.nextLine();
System.out.println("What is the body length?");
String bodyLength = scanner.nextLine();
Monkey monkey4 = new Monkey(name, gender, age, weight, acquisitionDate, acquisitionCountry, trainingStatus, reserved, inServiceCountry, species, tailLength, height, bodyLength);
monkeyList.add(monkey4);
System.out.println("Your entry has been added to the Monkey List.");
}
public static void reserveAnimal(Scanner scanner) {
scanner.nextLine();
System.out.println("Enter animal type: ");
String animalType = scanner.nextLine();
if (animalType.equalsIgnoreCase("Monkey")) {
System.out.println("Enter the monkey's acquisition country: ");
String country = scanner.nextLine();
for (Monkey obj: monkeyList) {
if (obj.getAcquisitionLocation().equalsIgnoreCase(country)) {
obj.setReserved(true);
System.out.println("This monkey is now reserved.");
return;
}
}
}
}
public static void printAnimals(char option) { // print options for dogList, monkeyList, all available animals
if (option == '4') {
System.out.println(dogList);
}
else if (option == '5') {
System.out.println (monkeyList);
}
else if (option == '6') {
for (int i = 0; i < dogList.size(); i++) {
if (dogList.get(i).getTrainingStatus().equals("in service") && dogList.get(i).getReserved()==false) {
System.out.println(dogList.get(i));
}
}
for (int i = 0; i < monkeyList.size(); i++) {
if (monkeyList.get(i).getTrainingStatus().equals("in service") && monkeyList.get(i).getReserved()==false) {
System.out.println(monkeyList.get(i));
}
}
}
}
}
我尝试搜索有关实现 toString 方法的信息，看看我是否能弄清楚，但没有成功。
DogDog@Override // <- technically optional, but very recommended
public String toString() {
return "What you want to show up when printing a Dog";
}
此方法返回的任何内容都会在打印
Dog