从void返回字符串

Question

hello I have this programming assignment where I have to use the functions they gave us, as they give it to us to use, the problem i am encountering is the fact this has to be void and I am not allowed to use System.out.println(); either so my question is how to i return the exception without changing the method header or it using System.out.println();?

public void deleteItem(String itemID){
    try {
        index = Change.indexOf(itemID);
        StockItems.remove(index);
        Change.remove(index);
    }
    catch (IndexOutOfBoundsException e) {
        System.out.println("ITEM " + itemID + " DOES NOT EXIST!");
    }
}

Answer 1

You can change your method signature and throw an exception

public void deleteItem(String itemID) throws Exception{
    try {
        index = Change.indexOf(itemID);
        StockItems.remove(index);
        Change.remove(index);
    }catch (IndexOutOfBoundsException e) {
        Exception ex = new Exception("ITEM " + itemID + " DOES NOT EXIST!");
        throw ex;
    }
}

Once done you can get your error message like this

try{
    xxx.deleteItem("your itemID");
}catch(Exception e){
    // You will read your "ITEM " + itemID + " DOES NOT EXIST!" here
    String yourErrorMessage = e.getMessage();
}

Answer 2

public void deleteItem(String itemID){
    try {
        index = Change.indexOf(itemID);
        StockItems.remove(index);
        Change.remove(index);
    }
    catch (IndexOutOfBoundsException e) {
        throw new IndexOutOfBoundsException( "ITEM " + itemID + " DOES NOT EXIST!");
    }
}


    public void deleteItem(String itemID)throws IndexOutOfBoundsException{

        index = Change.indexOf(itemID);
        StockItems.remove(index);
        Change.remove(index);

   } 

You cant return exceptions . Exceptions are thrown from the methods , you can use keyword throw for that.try above methods to throw exceptions from methods

Answer 3

In your catch block do this:

catch (IndexOutOfBoundsException e) {
       throw new IndexOutOfBoundsException("ITEM " + itemID + " DOES NOT EXIST!");
}

You don't need to add a throw declaration to your method, since IndexOutOfBoundsException is a RuntimeException.

Where ever you call the function you can add a catch block to read the error message like this:

catch (IndexOutOfBoundsException ex) {
      System.out.println(ex.getMessage());
}

Answer 4

Well, if the method is used incorrectly (without validation of the index), maybe it should throw an exception?

You can remove the try-catch block completely. IndexOutOfBoundsException is a runtime exception, so it does not require the throws IndexOutOfBoundsException syntax.

However, if you want the exception to be less cryptic, you can wrap it with your own RuntimeException :

public void deleteItem(String itemID){
    try {
        index = Change.indexOf(itemID);
        StockItems.remove(index);
        Change.remove(index);
    }
    catch (IndexOutOfBoundsException e) {
        throw new RuntimeException("Invalid item ID: " + itemID, e);
    }
}

Answer 5

Remove try..catch block and modify your function as

public void deleteItem(String itemID) throws IndexOutOfBoundsException{
         index = Change.indexOf(itemID);
        StockItems.remove(index);
        Change.remove(index);
}

Add try catch where you call this method and use System.out.println("ITEM " + itemID + " DOES NOT EXIST!"); there.

Ya even if you do not add throws to this method but put call of deleteItem in try catch block will work.