Question

所以我通过帮助解决了大部分问题，但是现在当我尝试正确打印IntegerSet时它没有改变。

我不确定为什么会出现这种类型的问题，可能是因为测试很糟糕？

This is how it remains. 

setA: IntegerSet@1893c911  // Any ideas why this happens?
setB: IntegerSet@e7587b2   // And this?
1) insertElement into setA
2) deleteElement from setA
3) insertElement into setB
4) deleteElement from setB
5) intersection of setA and setB
6) union of setA and setB
7) equality of setA and setB
Select from the menu above (or 0 to exit):

这是类代码：

int [] a;  // holds a set of numbers from 0 - 100

          public IntegerSet () {
            // an empty set, all a[i] are set to 0
            a = new int [101];
          }

          // A constructor that copies from an existing set.
          public IntegerSet (IntegerSet existingSet) {
            a = new int [101];
            for(int i=0; i<a.length; i++)
              a[i] = existingSet.a[i];
          }

          public void deleteElement(int i) {
            if ((i >= 0) && (i < a.length))
              a[i] = 0;  // set to 1
          }

          public void insertElement(int i) {
            if ((i >= 0) && (i < a.length))
              a[i] = 1;  // set to 1
          }

          public boolean isSet(int i) {
            return (a[i] == 1);
          }

          public int lengthOfArray(){
              return this.a.length;
        }

          public static IntegerSet union(IntegerSet otherSet, IntegerSet nextSet) {

                for(int i=0; i<otherSet.length(); i++) {
                  if (otherSet.isSet(i))
                    nextSet.insertElement(i);
                }

                return nextSet;
              }

              public static IntegerSet intersection(IntegerSet otherSet, IntegerSet nextSet) {

                for(int i=0; i<otherSet.length(); i++) {
                  if (!otherSet.isSet(i))
                    nextSet.deleteElement(i);
                }

                return nextSet;
              }



          // return true if the set has no elements
          public boolean isEmpty() {
            for (int i=0; i<a.length; i++)
              if (isSet(i)) return false;
            return true;
          }

          // return the 'length' of a set
          public int length() {
            int count = 0;
            for (int i=0; i<a.length; i++)
              if (isSet(i))
                count++;
            return count;
          }

          // Print a set to System.out
          public void setPrint() {
            System.out.print("[Set:");

            if (isEmpty())
              System.out.print("---");

            for (int i=0; i<a.length; i++) {
              if (isSet(i))
                System.out.print(" " + i);
            }

            System.out.print("]\n");
          }

          // return true if two sets are equal
          public boolean isEqualTo(IntegerSet otherSet) {
            for(int i=0; i<a.length; i++) {
              if (otherSet.isSet(i) != isSet(i))
                return false;
            }
            return true;
          }

测试代码：

import java.util.Scanner;

public class IntegerSetTest {

    public static void main(String args[]) {

        IntegerSet setA = new IntegerSet();
        IntegerSet setB = new IntegerSet();

        Scanner scan = new Scanner(System.in);
        int input;

        do {            
            // Just for formatting purposes...
            System.out.println();            
            System.out.println("setA: " + setA);
            System.out.println("setB: " + setB);
            System.out.println("1) insertElement into setA");
            System.out.println("2) deleteElement from setA");
            System.out.println("3) insertElement into setB");
            System.out.println("4) deleteElement from setB");
            System.out.println("5) intersection of setA and setB");
            System.out.println("6) union of setA and setB");
            System.out.println("7) equality of setA and setB");
            System.out.println("Select from the menu above (or 0 to exit): ");
            input = scan.nextInt();

            switch(input) {
                case 1: 
                    System.out.print("Enter an element to insert into setA: ");
                    setA.insertElement(scan.nextInt());
                    break;
                case 2:
                    System.out.print("Enter an element to delete from setA: ");
                    setA.deleteElement(scan.nextInt());                  
                    break;
                case 3:    
                    System.out.print("Enter an element to insert into setB: ");
                    setB.insertElement(scan.nextInt());                 
                    break;
                case 4:
                    System.out.print("Enter an element to delete from setB: ");
                    setB.deleteElement(scan.nextInt());                  
                    break;
                case 5:    
                    System.out.println("The intersection of setA and setB is: " + IntegerSet.intersection(setA, setB));
                    break;
                case 6:
                    System.out.println("The union of setA and setB is: " + IntegerSet.union(setA, setB));
                    break;
                case 7:
                    System.out.println("setA and setB are " + (setA.isEqualTo(setB) ? "" : "un") + "equal");
                    break;
                default:
                    if (input != 0) {
                        System.out.println("\n*** Error, invalid input! ***\n");
                    }
            }          
        }while(input != 0);
    }

}

Answer 1

当您尝试输出对象时......

System.out.println("setA: " + setA);

您正在尝试将对象转换为String。为了做到这一点：

字符串转换是通过方法toString实现的，由Object定义并由Java中的所有类继承。（docs.oracle.com）

...您需要覆盖课程IntegerSet中的toString(...) method：

    public String toString() {
        // Maybe you should use java.lang.StringBuilder instead
        String returnValue = "[Set:";

        if (isEmpty())
          returnValue += "---";

        for (int i=0; i<a.length; i++) {
          if (isSet(i))
            returnValue += " " + i;
        }

        returnValue += "]\n";

        return returnValue;
    }

Answer 2

您需要为toString()编写一个IntegerSet方法，创建一个String，其中包含您希望对象的表示形式。 toString()的默认实现打印出您看到的字符串类型。

Answer 3

IntegerSet@1893c911  // Any ideas why this happens?

这表明您的IntegerSet类不会覆盖toString（）方法。所以它使用默认的toString实现来打印类和实例标识符。

您需要覆盖toString方法。 Arrays.toString（）可以很好地打印数组。

程序输出十六进制为IntegerSet没有任何输入？

3 个答案: