unmodifiableMap

whatsmars-javase-example/src/main/java/com/itlong/whatsmars/base/collection/Point.java

+package com.itlong.whatsmars.base.collection;
+
+/**
+ * Created by shenhongxi on 2016/6/14.
+ */
+public class Point {
+
+    private float x;
+    private float y;
+
+    public Point(float x, float y){
+        setLocation(x, y);
+    }
+    public void setLocation(float x, float y){
+        this.x = x;
+        this.y = y;
+    }
+
+    public float getX(){
+        return x;
+    }
+
+    public float getY(){
+        return y;
+    }
+}

whatsmars-javase-example/src/main/java/com/itlong/whatsmars/base/collection/UnmodifiableTest.java

+package com.itlong.whatsmars.base.collection;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Created by shenhongxi on 2016/6/14.
+ */
+public class UnmodifiableTest {
+
+    private Map<String, Point> startingLocations = new HashMap<String, Point>(3);
+
+    public UnmodifiableTest(){
+        startingLocations.put("LeftRook", new Point(1, 1));
+        startingLocations.put("LeftKnight", new Point(1, 2));
+        startingLocations.put("LeftCamel", new Point(1, 3));
+        //..more locations..
+    }
+
+    public Map<String, Point> getStartingLocations(){
+        return Collections.unmodifiableMap(startingLocations);
+    }
+
+    public static void main(String [] args){
+        UnmodifiableTest  pieceLocations = new UnmodifiableTest();
+        Map<String, Point> locations = pieceLocations.getStartingLocations();
+
+        Point camelLoc = locations.get("LeftCamel");
+        System.out.println("The LeftCamel's start is at [ " + camelLoc.getX() +  ", " + camelLoc.getY() + " ]");
+
+        //Try 1. update elicits Exception
+        try{
+            locations.put("LeftCamel", new Point(0,0));
+        } catch (java.lang.UnsupportedOperationException e){
+            System.out.println("Try 1 - Could not update the map!");
+        }
+
+        //Try 2. Now let's try changing the contents of the object from the unmodifiable map!
+        camelLoc.setLocation(0,0);
+
+        //Now see whether we were able to update the actual map
+        Point newCamelLoc = pieceLocations.getStartingLocations().get("LeftCamel");
+        System.out.println("Try 2 - Map updated! The LeftCamel's start is now at [ " + newCamelLoc.getX() +  ", " + newCamelLoc.getY() + " ]");       }
+}