Polymorphism: 多态性处理对象数组 Java

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英文:

Polymorphism: handling an array of objects java

问题

在这个程序中,我必须使用多态的概念。

我有1个名为Data的抽象超类,以及2个名为List和Single的子类。Single接受一个双精度值(构造函数:public Single(value))。List接受一个双精度数组(构造函数:List(double[] arr)),在我的主方法中,以下数组...

public static void main(String[] args) {

    Object[] mixedData = {
        new Single(2.4),
        "The data is 3.6",
        new List(new double[] {3.2,6.8}),
        "Nothing here at all",
        new List(new double[] {1.2,7.9,4.5}),
        "Anda 1 anda 2 anda 3",
        new Single(9.8)
    };

我必须使用以下方法将这个Object[]数组转换为Data[]数组:

public static Data[] convert(Object[] objects){
    final int MAX_LIST_SIZE = 10;
    //***** YOUR CODE HERE *****
    objects= new Object[MAX_LIST_SIZE];
    Data[] data= new Data[MAX_LIST_SIZE];
    data = (Data[]) objects;
    for(int i=0; i<data.length; i++) {
    
    }
    return null; //Dummy statement - replace it
}

在这个方法中,

  1. 我们必须确保两个数组具有相同的长度。

  2. 使用浅复制

  3. 如果有一个字符串(如果它包含一个数字),则将其更改为List对象,其中包含字符串中可以找到的所有数字(作为单独的标记)。使用Scanner扫描字符串以查找数字。非数字应该被忽略。

我的唯一疑问是,在mixedData数组中,如何判断是否包含字符串。

希望有人会回答。

英文:

In this program, I have to use the concept of polymorphism,

I have 1 abstract superclass named Data, and 2 subclasses named List and Single. Single accepts a double value(Constructor: public Single(value)). List accepts an array of doubles.( Constructor: List(double[] arr)), and in my main method, the following array,...

public static void main(String[] args) {

    Object[] mixedData = {
      new Single(2.4),
      &quot;The data is 3.6&quot;,
      new List(new double[] {3.2,6.8}),
      &quot;Nothing here at all&quot;,     
      new List(new double[] {1.2,7.9,4.5}),
      &quot;Anda 1 anda 2 anda 3&quot;,
      new Single(9.8) };

I have to convert this Object[] array into Data[] array using a method:

  public static Data[] convert(Object[] objects){
    final int MAX_LIST_SIZE = 10;
  //***** YOUR CODE HERE *****
    objects= new Object[MAX_LIST_SIZE];
    Data[] data= new Data[MAX_LIST_SIZE];
    data = (Data[]) objects;
    for(int i=0; i&lt;data.length; i++) {
    	

    }
    return null; //Dummy statement - replace it
  }

In this method,

1)we have to make sure that both arrays are of same length.

2)Use shallow copy

3)If there is a String(if it contains a number), then change it to List object, containing all the numbers that can be found(as separate tokens) in the String. Use a Scanner to scan the String for
numbers. Non-numbers should be ignored.

My Only doubt is that, in mixedData array, how can I find if it contains a String.

hope someone will answer.

答案1

得分: 1

以下是您代码中的注释部分的中文翻译:

public static Data[] convert(Object[] objects){
    // 如果对象数组包含超过10个元素,应该怎么处理?
    // final int MAX_LIST_SIZE = 10;
    
    // 在这里你清空了输入对象的内容,为什么?
    // objects= new Object[MAX_LIST_SIZE]; 
    
    // 将数据数组的长度设置为输入对象数组的长度
    Data[] data= new Data[objects.length];
    
    // 这是不能这样做的
    // data = (Data[]) objects; 
    
    for(int i=0; i&lt;objects.length; i++) {
        if(objects[i] instanceof Single) {
            data[i] = (Single) objects[i];
        }else if(objects[i] instanceof List) {
            data[i] = (List) objects[i];
        }else if(objects[i] instanceof String) {
            String string = (String) objects[i];
            // 使用Scanner查找所有的double值
            // 将这些double值添加到一个列表中
            // 将该列表添加到data[i]
        }
    }
    return data;
}
英文:

I added some comments to your code to guide you through the solution.

public static Data[] convert(Object[] objects){
    // If the objects array contains more than 10 elements what to do?
	// final int MAX_LIST_SIZE = 10;
    
    // Here you clear the content of the input objects, why?
    //objects= new Object[MAX_LIST_SIZE]; 
    
	// Set the length of data to the length of the input object array
    Data[] data= new Data[objects.length];
    
    // This cannot be done
    // data = (Data[]) objects; 
    
    for(int i=0; i&lt;objects.length; i++) {
    	if(objects[i] instanceof Single) {
    		data[i] = (Single) objects[i];
    	}else if(objects[i] instanceof List) {
    		data[i] = (List) objects[i];
    	}else if(objects[i] instanceof String) {
    		String string = (String) objects[i];
    		// Find all doubles with Scanner
            // Add the doubles to a List
    		// Add the List to data[i]
    	}
    }
    return data;
  }

答案2

得分: 1

  1. 由于这两个数组的长度相同,您需要决定如何处理不包含小数的数组元素。例如,内联的字符串对象 &quot;Nothing here at all&quot; 不包含任何数字值,因此一旦我们处理字符串,它将返回一个空值。

  2. 浅复制:由于该字段是原始类型(double),请使用等号运算符将其值分配给右侧索引处的数组。

  3. 您可以轻松更改代码以实现使用 Scanner 扫描字符串以查找所需的数字。创建一个新的 Scanner 对象,并将要处理的字符串传递给构造函数。

英文:
  1. Since both arrays are of same length, you have to decide how to handle an array element that doesn't contain a decimal number. For example, the interned String object &quot;Nothing here at all&quot; doesn't contain any numerical values, so once we process the string, it will return a null value.

  2. Shallow copy: since the field is a primitive type (double), use the = operator to assign its value to the array at the right index.

  3. You can change the code easily to implement the use of a Scanner to scan the String for numbers as required. Create a new scanner object and pass the string you're processing in the constructor.

/**
 * Output:
 * Single obj: 2.4
 * Single obj: 3.6
 * List obj: 3.2 6.8
 * Data obj: null
 * List obj: 1.2 7.9 4.5
 * List obj: 1.0 2.0 3.0
 * Single obj: 9.8
 *
 * @author martinfall
 */
public class TestData {

    public static void main(String[] args) {
        // Given
        Object[] mixedData = {
            new Single(2.4),
            &quot;The data is 3.6&quot;,
            new List(new double[]{3.2, 6.8}),
            &quot;Nothing here at all&quot;,
            new List(new double[]{1.2, 7.9, 4.5}),
            &quot;Anda 1 anda 2 anda 3&quot;,
            new Single(9.8)};

        // Convert mixedData and assign the result to a Data array
        Data[] arr = convert(mixedData);

        // Print to console (Not required but helpful to see the output of each obj)
        for (Data datum : arr) {
            if (datum instanceof Single) {
                System.out.print(&quot;Single obj: &quot;);
                System.out.println(((Single) datum).value); // Can encapsulate
            } else if (datum instanceof List) {
                System.out.print(&quot;List obj: &quot;);
                for (double num : ((List) datum).arr) {
                    System.out.print(num + &quot; &quot;);
                }
                System.out.println();
            } else {
                // Since required that both arrays be equal size,
                // not sure how to handle an element of mixedData that doesn&#39;t
                // contain any decimal numbers
                System.out.println(&quot;Data obj: &quot; + datum);
            }
        }
    }

    public static Data[] convert(Object[] objects) {
        // Find the length of objects and assign it to MAX_LIST_SIZE
        final int MAX_LIST_SIZE = objects.length;

        // Create a new array of Data objects using the length of objects
        Data[] arr = new Data[MAX_LIST_SIZE];

        // Loop throught the array and copy each element as required
        for (int i = 0; i &lt; MAX_LIST_SIZE; i++) {
            if (objects[i] instanceof Single) {
                arr[i] = (Data) objects[i]; // Shallow copy
            } else if (objects[i] instanceof List) {
                arr[i] = (Data) objects[i];
            } else if (objects[i] instanceof String) {
                // Since both arrays have to be the same length, we have to add
                // the null value that is returned if a string doesn&#39;t contain
                // a numerical value
                arr[i] = processString((String) objects[i]);
            }
        }
        return arr;
    }

    public static Data processString(String str) {
        // Regular expression to match double values
        String regex = &quot;^[-+]?\\d*(\\.\\d+)?$&quot;;
        // Counter variable to use to find out if list or single is returned
        int count = 0;
        // Create a blank Data variable
        Data d = null;
        // Split the String
        String[] split = str.split(&quot; &quot;);

        // Determine if Single or List
        for (String s : split) {
            if (s.matches(regex)) {
                count++;
            }
        }

        // If count is 1, return a Single
        if (count == 1) {
            for (String s : split) {
                if (s.matches(regex)) {
                    d = new Single(Double.parseDouble(s));
                }
            }
        } else if (count &gt; 1) {
            // Create a new array as large as count
            double[] arr = new double[count];
            // Index of arr
            int arrIndex = 0;
            for (String s : split) {
                if (s.matches(regex)) {
                    arr[arrIndex] = Double.parseDouble(s);
                    arrIndex++;
                }
            }
            d = new List(arr);
        }
        return (Data) d;
    }
}

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  • 本文由 发表于 2020年7月29日 08:50:53
  • 转载请务必保留本文链接:https://go.coder-hub.com/63144772.html
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