程序輸出十六進制爲IntegerSet沒有任何輸入？

Question

所以我解決了大部分問題，有了幫助，但是現在當我嘗試正確地打印IntegerSet時，它不會改變。

我不知道爲什麼會出現這種類型的問題，也許是因爲測試很糟糕？

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): 

這是類代碼：

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; 
      } 

測試代碼：

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

當您嘗試輸出你的對象......

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

你試圖將對象轉換爲String。爲了做到這一點：

字符串轉換通過toString方法實現，由Object定義並由Java中的所有類繼承。 （docs.oracle.com）

...你需要重寫toString(...) method在IntegerSet類：

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

你需要寫一個toString()方法IntegerSet創建你想爲表示一個String您對象。 toString()的默認實現將打印出您所看到的字符串類型。

Answer 3

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

這表明你的IntegerSet類不會覆蓋toString（）方法。所以它使用默認的toString實現來打印類和實例標識符。

您需要重寫toString方法。 Arrays.toString（）可以很好地打印數組。