diff --git a/src/exception/NodeDoesNotExistException.java b/src/exception/NodeDoesNotExistException.java
new file mode 100644
index 0000000..7940626
--- /dev/null
+++ b/src/exception/NodeDoesNotExistException.java
@@ -0,0 +1,13 @@
+package exception;
+
+public class NodeDoesNotExistException extends Exception {
+	public String message;
+	/**
+	 * generated ID
+	 */
+	private static final long serialVersionUID = 6905916248289513991L;
+	
+	public NodeDoesNotExistException(String message) {
+		this.message = message;
+	}
+}
diff --git a/src/exception/NodeDoesNotHavePredecessor.java b/src/exception/NodeDoesNotHavePredecessor.java
new file mode 100644
index 0000000..157974f
--- /dev/null
+++ b/src/exception/NodeDoesNotHavePredecessor.java
@@ -0,0 +1,9 @@
+package exception;
+
+public class NodeDoesNotHavePredecessor extends Exception {
+	public String message;
+	
+	public NodeDoesNotHavePredecessor(String message) {
+		this.message = message;
+	}
+}