我搜索了整个论坛，找不到我要找的东西。我正在为学校做作业，我需要实施一些方法。我做了大部分，得到了我需要的输出。但是，我在实现笛卡尔积 (xproduct) 方法时遇到了麻烦。
到目前为止，这是我的代码：
import java.util.*;
public class Set
{
private ArrayList<String>elements;
/**
* creates an empty set
*/
public Set()
{
elements = null;
}
/**
* creates a set using the elements of the ArrayList s.
* @param s the ArrayList whose elements are used to create this set.
* @throws IllegalArgumentException if s contains duplicity.
*/
public Set(ArrayList<String> s)
{
int i;
elements = new ArrayList<String>();
for(i=0;i<s.size();i++)
{
if(elements.contains(s.get(i)))
{throw new IllegalArgumentException("Set(ArrayList<String>)duplicity not allowed in sets");}
elements.add(s.get(i));
}
}
/**
* creates a set using the elements of the array s.
* @param s the array whose elements are used to create this set.
* @throws illegalArgumentException if s contains duplicity.
*/
public Set(String[] s)
{
int i;
elements = new ArrayList<String>();
for(i=0; i<s.length; i++)
{
if (elements.contains(s[i]))
{throw new IllegalArgumentException("Set(String[]):duplicity not allowed in sets");}
elements.add(s[i]);
}
}
/**
* determines whether a set contains the specified element
* @param elt an element
* @return true if elt is an element of this set; otherwise, false
*/
public boolean isElement(String elt)
{
return elements.contains(elt);
}
/**
* determines the size of this set.
* @return the size of this set.
*/
public int cardinality()
{
return elements.size();
}
/**
* computes the intersection of this set and the
* specified set.
* @param s a set
* @return a set representing the intersection of this set
* and s.
*/
public Set intersect(Set s)
{
int i;
ArrayList<String> result = new ArrayList<String>();
for (i=0;i<s.cardinality();i++)
{
if (this.isElement(s.elements.get(i)))
{result.add(s.elements.get(i));}
}
return new Set(result);
}
/**
* computes the union of this set and the specified set.
* @param s a sets
* @return a set representing the union of this set
* and s.
*/
public Set union(Set s)
{
int i;
ArrayList<String> result = new ArrayList<String>();
result.addAll(this.elements);
result.addAll(s.elements);
for(i=0;i<s.cardinality();i++)
{
if (this.isElement(s.elements.get(i)))
{result.remove(s.elements.get(i));}
}
return new Set(result);
}
/**
* computes the difference between this set and the
* specified set.
* @param s a set
* @return a set representing the difference between
* this set and s.
*/
public Set diff(Set s)
{
int i;
ArrayList<String> result = new ArrayList<String>();
result.addAll(this.elements);
for(i=0;i<s.cardinality();i++)
{
if (this.isElement(s.elements.get(i)))
{result.remove(s.elements.get(i));}
}
return new Set(result);
}
/**
* computes the symmetric difference between this set
* and the specified set.
* @param s a set
* @return a set representing the symmetrical difference
* between this set and s.
*/
public Set symDiff(Set s)
{
int i;
ArrayList<String> result = new ArrayList<String>();
result.addAll(this.elements);
result.addAll(s.elements);
for(i=0;i<s.cardinality();i++)
{
if (this.isElement(s.elements.get(i)) && s.isElement(this.elements.get(i)))
{result.remove(this.elements.get(i));
result.remove(s.elements.get(i));}
}
return new Set(result);
}
/**
* computes the Cartesian product for this set
* and the specified set.
* @param s a set
* @return a set representing the Cartesian product
* of this set and s.
*/
public Set xProduct(Set s)
{
int i;
ArrayList<String> result = new ArrayList<String>();
result.addAll(this.elements);
result.addAll(s.elements);
}
/**
* determines whether a set is empty
* @return true if this set is empty; otherwise, false
*/
public boolean isEmpty()
{
return elements.isEmpty();
}
/**
* determines whether this set is equal to the specified
* set.
* @param s a set
* @return true if this set is equal to s; otherwise, false
*/
public boolean equals(Set s)
{
return elements.equals(s.elements);
}
/**
* determines whether this set is a subset of the specified set.
* @param s a set
* @return true if this set is a subset of s; otherwise, false
*/
public boolean subset(Set s)
{
return elements.containsAll(s.elements);
}
/**
* determines whether this set is a proper subset of the specified set.
* @param s a set
* @return true if this set is a proper subset of s; otherwise, false
*/
public boolean properSubset(Set s)
{
if(elements.equals(s.elements) && elements.containsAll(s.elements))
{return false;}
else{
return true;
}
}
/**
* returns a string {x1,x2,...,xn} representing this set,
* where x1,x2,...,xn are elements of this set.
* @return a string representation of this set formatted
* as specified.
*/
@Override
public String toString()
{
return "{"+this.elements+"}";
}
public static void main(String[] args)
{
String[]a1 = {"2","4","6","8"};
String[]a2 = {"2","3","5","7"};
String[]a3 = {"1","3","5"};
Set s1 = new Set(a1);
Set s2 = new Set(a2);
Set s3 = new Set(a3);
System.out.print("S1 ="); System.out.printf("%s",s1);
System.out.println();
System.out.print("S2 ="); System.out.printf("%s",s2);
System.out.println();
System.out.print("S3 ="); System.out.printf("%s",s3);
System.out.println();System.out.println();
System.out.println("(S1 \u222A S2:)");
System.out.printf("%s \u222A %s = %s%n",s1,s2,s1.union(s2));
System.out.println();
System.out.println("(S1 \u2296 S2) \u222a (S1 \u2229 S2) \u222a (S2 \u2296 S1)");
System.out.printf("%s \u2296 %s \u222a %s \u2229 %s \u222a %s \u2296 %s = %s%n",s1,s2,s1,s2,s2,s1,s1.diff(s2).union(s1.intersect(s2).union(s2.diff(s1))));
//Cartesian Product of s1 and s2
//Cartesian product of s2 and s1
}
}
任何指导将不胜感激。