java - do while string is NOT null or empty

Question

OK so here is some logic thinking... What I am trying to do is loop through strings until I hit a null/empty string.. then STOP. All while putting those strings inside a string array...

Here is a sample of the code. I know it's wrong but hopefully to give you an idea of what I am trying to achieve:

int i;
wepN = new String[100];
int wepQty = 0;
boolean anyLeft = true;
while (anyLeft == true) {
for(i = 0;i < 100;i++) {
    if (data.getItems().get(i).getName() == null) {
        anyLeft = false;
        System.out.println(data.getItems().get(i).getName() + " -NO MOARE");
    }
        wepN[i] = data.getItems().get(i).getName();
        wepQty++;

}
}

"No moare"! Was that a deliberate typo? Do you speak Maineglish? In other words, are/were you from Maine. e.g., close the doare. That's a pretty flowah. — Blessed Geek
– Blessed Geek, Commented Jul 21, 2010 at 4:06
You likely want to store the value of data.getItems() so you're only calling it once. It's likely to be a very expensive operation. — Gunslinger47
– Gunslinger47, Commented Jul 22, 2010 at 22:44

jayshao · Accepted Answer · 2010-07-21 04:00:58Z

2

You can use break to exit a for loop, same as you would a switch statement:

String[] wepN = new String[100];                        
int wepQty = 0;

for (int i=0; i < wepN.length; i++) {
    if (data.getItems().get(i).getName() == null || "".equals(data.getItems().get(i).getName())) {
        System.out.println(data.getItems().get(i).getName() + " -NO MOARE");
        break;
    }
    wepN[i] = data.getItems().get(i).getName();
    wepQty++;
}

answered Jul 21, 2010 at 4:00

jayshao

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2 Comments

Gunslinger47 Over a year ago

You can test if a String is equal to "" by saying str.isEmpty().

jayshao Over a year ago

@Gunslinger47 while you can call str.isEmpty() and in this case since we do a null check first it's safe, it's still a good habit in a lot of cases to prefer the older "".equals() since it's always null-safe and String interning means it's not really any less efficient.

user268396 · Accepted Answer · 2010-07-21 03:55:08Z

0

Numerous ways:

String currentName;
for(i=0;i<100;++i) {
  currentName=data.getItems().get(i).getName();
  if(currentName == null || currentName.length() ==0) {
    break;
  }
  // continue with old code here
}

If you don't like explicit breaks:

String currentName;
while(anyLeft) {
  currentName=data.getItems().get(i).getName();
  anyLeft= currentName != null && currentName.length() > 0;
  if(anyLeft) {
     // continue with old code here
  }
}

answered Jul 21, 2010 at 3:55

user268396

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Comments

mhshams · Accepted Answer · 2010-07-21 03:55:37Z

0

why you need to use while here?

how about:

for (int i = 0; i < 100 && data.getItems().get(i).getName() != null; i++ {
        wepN[i] = data.getItems().get(i).getName();
        wepQty++;
}

or

int i = 0;
while (data.getItems().get(i).getName() != null && i < 100) {
            wepN[i] = data.getItems().get(i).getName();
            wepQty++;
            i++
}

answered Jul 21, 2010 at 3:55

mhshams

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2 Comments

Gunslinger47 Over a year ago

wepQty and i are always equal. Thus, i is unnecessary.

Gunslinger47 Over a year ago

My comment on NullUserException's answer also applies here. stackoverflow.com/questions/3296165/…

S73417H · Accepted Answer · 2010-07-21 04:18:28Z

0

Something like this is what you are after:

Collection<String> original = new LinkedList<String>();
original.add("String1");
original.add("String2");
original.add("");
original.add(null);
original.add("String 3");

Collection<String> tested = new LinkedList<String>();

for(String string: original) {
  if(null != string && !string.isEmpty()) {
    tested.add(string);
  }
}

String[] stringArray = tested.toArray(new String[tested.size()]);

I would argue not to use array at all and just stick to the Collection type however.

If you want to stop on the first occurance of a null or empty string just do:

if(null != string && !string.isEmpty()) {
    tested.add(string);
  } else {
    break;
}

edited Jul 21, 2010 at 4:18

answered Jul 21, 2010 at 3:53

S73417H

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1 Comment

jayshao Over a year ago

I wouldn't recommend jumping straight to a Collection - you could have an interface that requires String[], or have some other reason for preferring it.

Blessed Geek · Accepted Answer · 2010-07-21 04:37:42Z

There are a few considerations depending on whether the original was a collection.

If you had an array Data[] data,

String[] dataCopy = new String[data.length];
int i = 0;
for (Data datum: data){
 if (datum==null)break;
 dataCopy[i++] = datum;
}

But that is not optimal because you would be assigning more array cells than necessary if the original data had 100 cells but the 50th cell is where the empty string is found.

Using an ArrayList would let the JVM manage the expansion of cells, so that at the end of it you just convert the ArrayList to an array using toArray(). It's not a conversion really, but toArray withdraws the internally managed array from the ArrayList.

ArrayList<String> dataList = new ArrayList<String>(data.length);
for (Data datum: data){
 if (datum==null)break;
 dataList.add(datum);
}
String[] dataCopy = {};
dataCopy = datalist.toArray(dataCopy);

Or if the array you are processing is a member of data:

ArrayList<String> dataList = new ArrayList<String>(data.length);
for (Data datum: data.getItems()){
 String name = datum.getName();
 if (name==null)break;
 dataList.add(name);
}
String[] dataCopy = {};
dataCopy = datalist.toArray(dataCopy);

Or if the original data structure implements Iterable. Let's say the class of items is Item.

Iterator<Item> itemit = data.getItems().iterator();
ArrayList<String> dataList = new ArrayList<String>(data.length);
while(itemit.hasNext()){
  String name = itemit.next().getName;
  if (name==null)break;
  dataList.add(name);
}
String[] dataCopy = {};
dataCopy = datalist.toArray(dataCopy);

If it implements Iterable, it can be used in a for each loop.

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