Implemented multi Iterator class that combines multiple iterators as one.

src/zutil/struct/MultiIterator.java

@@ -0,0 +1,77 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2020 Ziver Koc
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package zutil.struct;
+
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.NoSuchElementException;
+import java.util.Queue;
+
+/**
+ * This class is a wrapper that combine multiple Iterators of same type.
+ * This class will start by iterating through the first Iterator until the
+ * end of it has been reach and then the next iterator will be used until
+ * all iterators no longer has any items.
+ */
+public class MultiIterator<T> implements Iterator<T> {
+    private Queue<Iterator<T>> queue = new LinkedList<>();
+
+
+    public void addIterator(Iterator<T> it) {
+        queue.add(it);
+    }
+
+
+    @Override
+    public boolean hasNext() {
+        if (queue.isEmpty())
+            return false;
+        else {
+            if (!queue.peek().hasNext()) {
+                queue.poll();
+                return hasNext();
+            }
+
+            return true;
+        }
+    }
+
+    @Override
+    public T next() {
+        if (!hasNext())
+            throw new NoSuchElementException("End of iterator has been reached.");
+        else {
+            return queue.peek().next();
+        }
+    }
+
+    @Override
+    public void remove() {
+        if (queue.isEmpty())
+            return;
+
+        queue.peek().remove();
+    }
+}

test/zutil/struct/MultiIteratorTest.java

@@ -0,0 +1,76 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2020 Ziver Koc
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package zutil.struct;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.NoSuchElementException;
+
+import static org.junit.Assert.*;
+
+public class MultiIteratorTest {
+
+    @Test(expected = NoSuchElementException.class)
+    public void emptyTest() {
+        MultiIterator<String> it = new MultiIterator<>();
+        assertEquals(false, it.hasNext());
+        it.next(); // NoSuchElementException
+    }
+
+    @Test
+    public void oneIteratorTest() {
+        MultiIterator<String> it = new MultiIterator<>();
+        it.addIterator(Arrays.asList("value1", "value2").iterator());
+
+        assertEquals(true, it.hasNext());
+        assertEquals("value1", it.next());
+
+        assertEquals(true, it.hasNext());
+        assertEquals("value2", it.next());
+
+        assertEquals(false, it.hasNext());
+    }
+
+    @Test
+    public void multiIteratorTest() {
+        MultiIterator<String> it = new MultiIterator<>();
+        it.addIterator(Arrays.asList("value1", "value2").iterator());
+        it.addIterator(Arrays.asList("value3", "value4").iterator());
+        it.addIterator(Arrays.asList("value5", "value6").iterator());
+
+        assertEquals("value1", it.next());
+        assertEquals("value2", it.next());
+
+        assertEquals(true, it.hasNext());
+        assertEquals("value3", it.next());
+        assertEquals("value4", it.next());
+
+        assertEquals("value5", it.next());
+        assertEquals("value6", it.next());
+
+        assertEquals(false, it.hasNext());
+    }
+}