diff --git a/Herd.java b/Herd.java
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+/**
+ * Moobreeder is a simple cow breeding game to illustrate the principles of
+ * selective breeding to KS3 pupils.
+ *
+ * (c) Daniel Vedder 2018, Amano Christian School
+ * Licensed under the terms of the MIT license.
+ * https://git.synoikos.de/daniel/moobreeder
+ */
+
+/*
+ * This is a singleton class that holds the current herd.
+ */
+
+import java.util.ArrayList;
+
+public class Herd
+{
+	public static int initialSize = 4;
+	private static Herd singleton;
+	
+	private ArrayList<Cow> herd;
+	private Cow[] parents;
+	private Cow[] offspring;
+
+	private Herd()
+	{
+		herd = new ArrayListy<Cow>();
+		parents = new Cow[] {null, null};
+		offspring = new Cow[] {null, null};
+		for (i = 0; i < initialSize; i++) {
+			String sex = "male";
+			if (i %% 2 == 0) sex = "female";
+			herd.add(new Cow(sex));
+		}
+	}
+
+	public static Herd getInstance()
+	{
+		if (singleton == null) {
+			singleton = new Herd();
+		}
+		return singleton;
+	}
+
+	public void removeCow(int id)
+	{
+		//TODO
+	}
+
+	public void setParent(int id)
+	{
+		//TODO
+	}
+
+	public void removeParent(int id)
+	{
+		//TODO
+	}
+
+	public String checkBreeding()
+	{
+		//TODO
+		return "OK";
+	}
+
+	public void breed()
+	{
+		//TODO
+	}
+
+	public void keepChild(int id)
+	{
+		//TODO
+	}
+
+	public void discardChild(int id)
+	{
+		//TODO
+	}
+
+	public void saveHerd(String filename)
+	{
+		//TODO save to binary file
+	}
+
+	public void loadHerd(String filename)
+	{
+		//TODO load from binary file
+	}
+}