如何在Java中的搜索函数（数组）中返回多个值

Question

I have a search function in a class that searches through an array by a String(Department of work) and a count. In the main the program will ask the user what category does he/she wants to search for. Example: library ; the program should give all the books that are in that specific department (there is a function that lets the user add books) The problem is that the program only returns one book and not the all the books that are associated within that Category.

Answer 1

Your function should not return an single index it should return a collection of indexes. For example.

public static Collection<Integers> Searchdep(EmployeeClass EmployeeArr[], String department, int size)  {
   List<Integer> intList = new ArrayList<Integer>();
   for(int i=0; i<size; i++)
   {
      if(EmployeeArr[i].Department.equals(department)) {
          intList.add(i);
      }
   }
   return intList;
}

Then in your main check for size of the collection, if it is zero that mean nothing was found. Theses the line need to change

index=EmployeeClass.SearchDep(EmpList,department,count);
JOptionPane.showMessageDialog(null,index);

to

Collection<Integer> returnedCollection = EmployeeClass.SearchDep(EmpList,department,count);
if(returnedCollection.isEmpty()){
   JOptionPane.showMessageDialog(null,"Nothing was found");     
} else {
   StringBuilder  str = new StringBuilder();
   for(Integer integer: returnedCollection){
       str.appened(EmpList[integer].ReturnStringInfo());
       str.appened(", ");
   }
   JOptionPane.showMessageDialog(null,"Indexed are : "+ str.toString());     
}

Answer 2

Just return an array of indices instead of a single index. For example:

public static List<Integer> Searchdep(EmployeeClass EmployeeArr[], String department, int size){
      List<Integer> result = new ArrayList<Integer>();
      for(int i=0; i<size; i++){
          if(EmployeeArr[i].Department.equals(department)){
              result.add(i);
          }
      }
      return result;
}

Answer 3

The best option here is to pass a Visitor action to apply to each employee found. In Java 8, this would be a lambda but in Java 6 or 7 this would be an anonymous inner class.

Then you might return the count found so you can detect when there was no matches.