从TreeMap删除条目，获取java.util.NoSuchElementException

Question

I am trying to remove some entries from TreeMap using some logic. This my code

TreeMap<String, Object> treeMap = someEntries();
Iterator<Entry<String, Object> iter = treeMap.entrySet().iterator();
Map.Entry<String, Object> entry = null;

while ((entry = iter.next()) != null) {
    if (!entry.getKey().contains(search)) {
        iter.remove();
    }
}

getting Exception:-

java.util.NoSuchElementException
    at java.util.TreeMap$PrivateEntryIterator.nextEntry(TreeMap.java:1113)
    at java.util.TreeMap$EntryIterator.next(TreeMap.java:1151)
    at java.util.TreeMap$EntryIterator.next(TreeMap.java:1146)

What is that Exception? This is the error during iteration. Please also suggest me a right way.

Answer 1

You should be checking with Iterator#hasNext() not Iterator#next() like so:

while (iter.hasNext()) {
    entry = iter.next();
    if (!entry.getKey().contains(search)) {
        iter.remove();
    }
}

Answer 2

You should be checking for the next element like this:

    TreeMap<String, Object> treeMap = someEntries();
    Iterator<Entry<String, Object>> iter = treeMap.entrySet().iterator();
    Entry<String, Object> entry;
    while (iter.hasNext()) {
        entry = iter.next();
        if (!entry.getKey().contains(search)) {
            iter.remove();
        }
    }

If you call iter.next() when there is no next element, the NoSuchElementException gets thrown.

Answer 3

When you traverse to the last element, the 'next' point is NULL, so you will get NoSuchElementException when you go to the end. Use the following code to have a try:

TreeMap<String, Object> treeMap = new TreeMap<String, Object>();
treeMap.put("a", 1);
treeMap.put("b", 2);
treeMap.put("c", 3);
treeMap.put("d", 4);
Iterator<Entry<String, Object>> iter = treeMap.entrySet().iterator();
Map.Entry<String, Object> entry = null;

while (iter.hasNext()) {
    entry = iter.next();
    System.out.println(entry.getKey());
    if (!entry.getKey().contains("a")) {
           iter.remove();
    }
}

System.out.println("-----");
iter = treeMap.entrySet().iterator();
while (iter.hasNext()) {
    entry = iter.next();
    System.out.println(entry.getKey());
}