java - 如何使用 Java 中的另一个对象创建一个对象？

Question

我正在定义 Dog 类的特征，该类包含定义其名称和年龄的实例数据，为此数据创建构造函数，setter-getter 方法等。我还有一个返回“狗年”值的方法（又名，七年乘以他们同等年龄的人类年）。我有一个驱动程序类 Kennel，它的主要方法实例化和更新这些 Dog 对象，并将它们打印出来。

在 Kennel 类中，我的最后一条语句中您可以看到一条评论，上面写着“在某个点查询”。即：//Dog dog3 = dog2.setName("Krypto"); 在评论中，我尝试创建一个名为“Kryto”的新 Dog 对象，同时分配其余的通过 setName 方法将 dog2 对象的数据传递给它。换句话说，我希望我的 dog3 对象具有 dog2 的所有特征，但名称除外。

实现这一目标的方法是什么？我知道我不能将对象用作参数，对吗？

这是我下面两个类的代码：

Kennel (Driver):

    public class Kennel {
    //instance data
    int age;
    public static void main(String[] args) {
        //dog objects
        Dog dog1 = new Dog("Bear", 3);
        Dog dog2 = new Dog("Bella", 7);
        
        //calling the method required to calculate the dog's human years, so that when I print these objects out, they actually have their traits
        //(that being, their "dogman" age.
        dog1.calcDogmanYears();
        dog2.calcDogmanYears();
        
        //output
        System.out.println(dog1);
        System.out.println(dog2);
        dog2.setName("Krypto");
        //Dog dog3 = dog2.setName("Krypto"); //INQUIRE AT SOME POINT
        System.out.println(dog2);

    }

}

狗：

public class Dog {
    //instance data
    String name;
    int age;
    
    //constructor (normal) to allow objects to have values by default (i.e. no requirement of forcing parameters down the methods from the driver class)
    public Dog()    {
        name = "";
        age = 0;
        return;
    }
    
    //constructor, keep in mind for future reference, that I used different variables to allow the constructor to be overloaded in a driver class to
    //follow Chapter 4's constructor Java syntax. We could've overloaded the constructor with formal parameters of the same name as the instance data
    //with the "this.(insert variable here)" modifier. I did this for shits and giggles.
    public Dog(String name, int age){
        this.name = name;
        this.age = age;
        return;
    }
    
    //method to convert dog to human years
    public int calcDogmanYears() {
        age = age * 7;
        return age;
    }
        
    //setters and getters for name
    public void setName(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
    
    //mutators and accessors for age}
    public void setAge(int age) {
        this.age = age;
    }
    public int getAge() {
        return age;
    }
    
    public String toString() {
        String result = "The name of the dog is " + name + ", and their age is " + age + " years old.";
        return result;
    }
}

标签： javaclassobjectconstructorcode-reuse

Answer 1

一种选择是使Dog类可克隆。克隆原件，然后name适当设置。

Dog dog3 = dog2.clone();
dog3.setName("Krypto");

犬舍（司机）类：

public class Kennel {
    //instance data
    int age;
    public static void main(String[] args) throws CloneNotSupportedException {
        //dog objects
        Dog dog1 = new Dog("Bear", 3);
        Dog dog2 = new Dog("Bella", 7);
        
        //calling the method required to calculate the dog's human years, so that when I print these objects out, they actually have their traits
        //(that being, their "dogman" age.
        dog1.calcDogmanYears();
        dog2.calcDogmanYears();
        
        //output
        System.out.println(dog1);
        System.out.println(dog2);
        dog2.setName("Krypto");
        Dog dog3 = dog2.clone();
        dog3.setName("Krypto"); //INQUIRE AT SOME POINT
        System.out.println(dog2);

    }

}

更新的狗类：

public class Dog implements Cloneable {
    //instance data
    String name;
    int age;
    
    //constructor (normal) to allow objects to have values by default (i.e. no requirement of forcing parameters down the methods from the driver class)
    public Dog()    {
        name = "";
        age = 0;
    }
    // Overriding clone() method of Object class
    public Dog clone() throws CloneNotSupportedException{  
    return (Dog) super.clone();  
    }
    
    public Dog(String name, int age){
        this.name = name;
        this.age = age;
    }
    
    //method to convert dog to human years
    public int calcDogmanYears() {
        age = age * 7;
        return age;
    }
        
    //setters and getters for name
    public void setName(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
    
    //mutators and accessors for age}
    public void setAge(int age) {
        this.age = age;
    }
    public int getAge() {
        return age;
    }
    
    public String toString() {
        String result = "The name of the dog is " + name + ", and their age is " + age + " years old.";
        return result;
    }
}

输出：

这只狗的名字叫熊，它们的年龄是21岁。
这只狗的名字叫贝拉，它们的年龄是49岁。
这只狗的名字叫Krypto，它们的年龄是49岁。