add lesson4 homework

lesson4/src/DoubleLinkedList.java

@@ -0,0 +1,119 @@
+import java.util.Iterator;
+import java.util.Objects;
+import java.util.function.Consumer;
+
+public class DoubleLinkedList<T> extends RelatedList {
+    private class Node<T> {
+        T c;
+        public Node(T c) {
+            this.c = c;
+        }
+
+        @Override
+        public String toString() {
+            return c.toString();
+        }
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (!(o instanceof Node)) return false;
+            Node<T> node = (Node) o;
+            return Objects.equals(c, node.c);
+        }
+
+        Node<T> prev;
+        Node<T> next;
+    }
+
+    private Node<T> head;
+    private Node<T> iterNext;
+
+    public DoubleLinkedList() {
+        head = null;
+        iterNext = head;
+    }
+
+
+    @Override
+    public void insert(Object c) {
+        Node<T> n = new Node<T>((T)c);
+        n.next = head;
+        if (head != null) {
+            head.prev = n;
+        }
+        head = n;
+        iterNext = head;
+    }
+
+
+    public T delete(T c) {
+        Node<T> current = head;
+
+        while (!current.c.equals(c)) {
+            if (current.next == null)
+                return null;
+
+            current = current.next;
+
+        }
+        if (current == head) {
+            head = head.next;
+            iterNext = head;
+        } else {
+            current.prev.next = current.next;
+            current.next.prev = current.prev;
+        }
+        return current.c;
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return head == null;
+    }
+
+    @Override
+    public T remove() {
+        if (isEmpty())
+            return null;
+        T temp = head.c;
+        head = head.next;
+        iterNext = head;
+        return temp;
+    }
+
+    @Override
+    public boolean contains(Object c) {
+        Node<T> n = new Node<>((T) c);
+        Node<T> current = head;
+        while (!current.equals(n)) {
+            if (current.next == null)
+                return false;
+            else
+                current = current.next;
+        }
+        return true;
+    }
+
+    @Override
+    public String toString() {
+        if (isEmpty()) return "[]";
+        Node<T> current = head;
+        StringBuilder sb = new StringBuilder("[");
+        while (current != null) {
+            sb.append(current);
+            current = current.next;
+            sb.append((current == null) ? "]" : ", ");
+        }
+        return sb.toString();
+    }
+
+    public boolean hasNext() {
+        return iterNext != null;
+    }
+
+    public T next() {
+        Node<T> toBeReturned = iterNext;
+        iterNext = iterNext.next;
+        return toBeReturned.c;
+    }
+}

lesson4/src/RelatedList.java

@@ -1,8 +1,8 @@
 import java.util.Objects;
 
 public class RelatedList<T> {
-    private class Node<T> {
-        T c;
+    protected class Node<T> {
+        private T c;
         Node<T> next;
         public Node(T c) {
             this.c = c;
@@ -20,7 +20,7 @@ public boolean equals(Object o) {
         }
     }
 
-    private Node<T> head;
+    protected Node<T> head;
 
     public RelatedList() {
         head = null;
@@ -56,7 +56,7 @@ public boolean contains(T c) {
         return true;
     }
 
-    public T delete(String name) {
+    public final T delete(String name) {
         Node<T> current = head;
         Node<T> previous = head;
         while (!(((Cat)current.c).getName()).equals(name)) {

lesson4/src/Relations.java

@@ -5,20 +5,28 @@
 
 public class Relations {
     public static void main(String[] args) {
-        RelatedList<Cat> rl = new RelatedList<>();
-        rl.insert(new Cat(1, "Barsik"));
-        rl.insert(new Cat(2, "Murzik"));
-        rl.insert(new Cat(4, "Kissik"));
-        System.out.println(rl);
-        System.out.println(rl.remove());
-        System.out.println(rl);
-        System.out.println(rl.contains(new Cat(2, "Murzik")));
+        DoubleLinkedList<Cat> dll = new DoubleLinkedList<>();
+        Cat c = new Cat(2, "Murzik");
+        dll.insert(new Cat(1, "Barsik"));
+        dll.insert(c);
+        dll.insert(new Cat(4, "Kissik"));
+//        System.out.println(dll);
+//        System.out.println(dll.delete(c));
+//        System.out.println(dll);
+//        System.out.println(dll.contains(new Cat(2, "Murzik")));
+
 
-        HashMap<String, String> map = new HashMap<>();
-        Set<Map.Entry<String, String>> set = map.entrySet();
-        Iterator<Map.Entry<String, String>> iter = set.iterator();
-        while (iter.hasNext()) {
-            System.out.println(iter.next().getKey() + iter.next().getValue());
+//        HashMap<String, String> map = new HashMap<>();
+//        Set<Map.Entry<String, String>> set = map.entrySet();
+//        Iterator<Map.Entry<String, String>> iter = set.iterator();
+//        while (iter.hasNext()) {
+//            System.out.println(iter.next().getKey() + iter.next().getValue());
+//        }
+
+        dll.insert(c);
+
+        while (dll.hasNext()) {
+            System.out.println(dll.next());
         }
     }
 }