我有两节课 Dog.java 以及 DogSerach.java 我想用hashmap打印狗的细节。我研究了这个问题的副本，根据键名从hashmap中获取字符串值，还研究了oracle文档http://docs.oracle.com/javase/tutorial/collections/interfaces/map.html，但还是想不通。
我在dogsearch.java中尝试过

for (String key: dogs.keySet()) {
            System.out.println("Registration number : " + key);
           System.out.println("Detail : " +  dogs.get(key));
           }

但我明白了

Registration number : 1003
Detail : Dog [name=Luca, breed=Labrador, registrationNumber=1003]
Registration number : 1002
Detail : Dog [name=Gracie, breed=Rottweiler, registrationNumber=1002]
Registration number : 1001
Detail : Dog [name=Max, breed=German Shepherd, registrationNumber=1001]

我想印成这样

Registration number: 1001
Name: Max
Breed: German Shepherd
... etc.

狗搜索.java

public class DogSearch {

    static Scanner scanner = new Scanner(System.in);
    public static void main(String[] args) {
        Map<String, Dog> dogs = new HashMap<String, Dog>();

        Dog max = new Dog("Max", "German Shepherd", "1001");
        Dog gracie = new Dog("Gracie", "Rottweiler", "1002");
        Dog luca = new Dog("Luca", "Labrador", "1003");

        dogs.put(max.getRegistrationNumber(), max);
        dogs.put(gracie.getRegistrationNumber(), gracie);
        dogs.put(luca.getRegistrationNumber(), luca);

        System.out.println("List of dogs by name: ");

        for (String key: dogs.keySet()) {
            System.out.println("Registration number : " + key);
            System.out.println("Breed : " +  dogs.get(key));

        }

    }
}

狗.java

class Dog {
    private String name;
    private String breed;
    private String registrationNumber;

    public Dog(String name, String breed, String registrationNumber) {
        this.name = name;
        this.breed = breed;
        this.registrationNumber = registrationNumber;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getBreed() {
        return breed;
    }

    public void setBreed(String breed) {
        this.breed = breed;
    }

    public String getRegistrationNumber() {
        return registrationNumber;
    }

    public void setRegistrationNumber(String registrationNumber) {
        this.registrationNumber = registrationNumber;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((breed == null) ? 0 : breed.hashCode());
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        result = prime * result + ((registrationNumber == null) ? 0 : registrationNumber.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Dog other = (Dog) obj;
        if (breed == null) {
            if (other.breed != null)
                return false;
        } else if (!breed.equals(other.breed))
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        if (registrationNumber == null) {
            if (other.registrationNumber != null)
                return false;
        } else if (!registrationNumber.equals(other.registrationNumber))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "Dog [name=" + name + ", breed=" + breed + ", registrationNumber=" + registrationNumber + "]";
    }
}