Converted everything to work with polymorphism

Added "Grootheid" to act as a parent to all children classes, it allows
the main "Weerstation" to update them all better and with cleaner code.

Grootheid.java

@@ -0,0 +1,86 @@
+import java.util.ArrayList;
+
+public class Grootheid
+{
+    // instance variables - replace the example below with your own
+    public double avg;
+    public double max;
+    public double min;
+    public double current;
+
+    //constructor
+    public Grootheid(){
+        avg = 0;
+        max = 0;
+        min = 0;
+        current = 0;
+    }
+    
+    //getters & setters
+    public double getCurrent() {
+        return current;
+    }
+
+    public void setCurrent(double current) {
+        this.current = current;
+    }
+
+    public double getMax() {
+        return max;
+    }
+
+    public void setMax(double max) {
+        this.max= max;
+    }
+
+    public double getMin() {
+        return min;
+    }
+
+    public void setMin(double min) {
+        this.min = min;
+    }
+
+    public double getAvg() {
+        return avg;
+    }
+
+    public void setAvg(double avg) {
+        this.avg = avg;
+    }
+    
+    //Methods
+    public void calculateMaxMinAvg(ArrayList<Double> laatste24uur){
+        double tempMax = 0;
+        double tempAvg = 0;
+        double tempMin = laatste24uur.get(0);
+        
+        for(double ms : laatste24uur){
+            if(ms > tempMax){
+                tempMax = ms;
+            }
+            if(ms <  tempMin){
+                tempMin = ms;
+            }
+            tempAvg += ms;
+        }
+        tempAvg /= laatste24uur.size();
+        
+        setMax(tempMax);
+        setMin(tempMin);
+        setAvg(tempAvg);
+    }
+
+    public void updateRecent(Measurement measurement1){
+
+    }
+    public void update24Hour(ArrayList<Measurement> measurement2){
+        
+    }
+    
+    public void display(){
+        GUIboard.writeUpperDigits(getCurrent());
+        GUIboard.writeLeftDigits(getMax());
+        GUIboard.writeRightDigits(getMin());
+    }
+}