change list to linkedlist so it builds in ci

Author: CatarinaGamboa

latte-umbrella/src/main/java/context/PermissionEnvironment.java

@@ -2,9 +2,9 @@
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
-import java.util.Stack;
 
 /**
  * Permission Environment class to store the permissions of the variables in scope
@@ -14,7 +14,7 @@ public class PermissionEnvironment {
 
     private static PermissionEnvironment instance;
 
-    private List<Map<SymbolicValue, UniquenessAnnotation>> map;
+    private LinkedList<Map<SymbolicValue, UniquenessAnnotation>> map;
 
 
     /**
@@ -27,7 +27,7 @@ public static PermissionEnvironment getInstance() {
     }
 
     private PermissionEnvironment() {
-        map = new Stack<Map<SymbolicValue, UniquenessAnnotation>>(); 
+        map = new LinkedList<Map<SymbolicValue, UniquenessAnnotation>>(); 
     }
 
     /**

latte-umbrella/src/main/java/context/SymbolicEnvironment.java

@@ -2,9 +2,9 @@
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
-import java.util.Stack;
 
 /**
  * Symbolic Environment class to store the variables to their symbolic values
@@ -17,7 +17,7 @@ public class SymbolicEnvironment {
 
 	int symbolic_counter = 0;
 
-    private List<Map<VariableHeapLoc, SymbolicValue>> symbEnv;
+    private LinkedList<Map<VariableHeapLoc, SymbolicValue>> symbEnv;
 
 	/**
 	 * Singleton instance
@@ -29,7 +29,7 @@ public static SymbolicEnvironment getInstance() {
 	}
 
 	private SymbolicEnvironment() {
-		symbEnv = new Stack<Map<VariableHeapLoc, SymbolicValue>>();
+		symbEnv = new LinkedList<Map<VariableHeapLoc, SymbolicValue>>();
 	}
 
 	public SymbolicValue addVariable(String var) {