Added testclass and implemented methods

src/search/breadthfirstsearch/EightPuzzleNode.java

@@ -0,0 +1,62 @@
+package search.breadthfirstsearch;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.IntStream;
+
+public class EightPuzzleNode implements Node
+{
+    private int[][] state;
+
+    public EightPuzzleNode(int[][] state) {
+        if (!isValidState(state))
+        {
+            throw new IllegalArgumentException("Allowed numbers are only 0-8 and they must exist uniquely.");
+        }
+
+        this.state = state;
+    }
+
+    @Override
+    public boolean isTargetReached(Node target) {
+        return Arrays.equals(this.state, ((EightPuzzleNode) target).state);
+    }
+
+    @Override
+    public List<Node> generateSuccessors() {
+        ArrayList<Node> successors = new ArrayList<>();
+
+        successors.add(new EightPuzzleNode(null));
+
+        return successors;
+    }
+
+    private boolean isValidState(int[][] state)
+    {
+        int[] numbers = Arrays.stream(state).flatMapToInt(IntStream::of).toArray();
+        int[] countOfNumbers = new int[9];
+
+        for (int i : numbers)
+        {
+            try
+            {
+                countOfNumbers[i]++;
+            }
+            catch (ArrayIndexOutOfBoundsException e)
+            {
+                return false;
+            }
+        }
+
+        for (int i : countOfNumbers)
+        {
+            if (i == 0 || i > 1)
+            {
+                return false;
+            }
+        }
+
+        return true;
+    }
+}