diff --git a/src/adap-b04/files/Directory.ts b/src/adap-b04/files/Directory.ts
index b1179030..9b6ff3a7 100644
--- a/src/adap-b04/files/Directory.ts
+++ b/src/adap-b04/files/Directory.ts
@@ -1,3 +1,4 @@
+import { IllegalArgumentException } from "../common/IllegalArgumentException";
 import { Node } from "./Node";
 
 export class Directory extends Node {
@@ -5,14 +6,24 @@ export class Directory extends Node {
     protected childNodes: Set<Node> = new Set();
 
     constructor(bn: string, pn: Directory) {
+        // precondition
+        IllegalArgumentException.assertIsNotNullOrUndefined(pn);
+        IllegalArgumentException.assertCondition(typeof bn === "string" && bn.length > 0, "basename must be at least one character long.");
+        
         super(bn, pn);
     }
 
     public add(cn: Node): void {
+        // precondition
+        IllegalArgumentException.assertCondition(!this.childNodes.has(cn), "Node mustn't exist to add it.");
+
         this.childNodes.add(cn);
     }
 
     public remove(cn: Node): void {
+        // precondition
+        IllegalArgumentException.assertCondition(this.childNodes.has(cn), "Node must exist to delete it.");
+
         this.childNodes.delete(cn); // Yikes! Should have been called remove
     }
 
diff --git a/src/adap-b04/files/File.ts b/src/adap-b04/files/File.ts
index 0e7aa84a..dbc5665c 100644
--- a/src/adap-b04/files/File.ts
+++ b/src/adap-b04/files/File.ts
@@ -1,5 +1,6 @@
 import { Node } from "./Node";
 import { Directory } from "./Directory";
+import { IllegalArgumentException } from "../common/IllegalArgumentException";
 
 enum FileState {
     OPEN,
@@ -11,15 +12,25 @@ export class File extends Node {
 
     protected state: FileState = FileState.CLOSED;
 
-    constructor(baseName: string, parent: Directory) {
-        super(baseName, parent);
+    constructor(bn: string, pn: Directory) {
+        // precondition
+        IllegalArgumentException.assertIsNotNullOrUndefined(pn);
+        IllegalArgumentException.assertCondition(typeof bn === "string" && bn.length > 0, "basename must be at least one character long.");
+        
+        super(bn, pn);
     }
 
     public open(): void {
+        // precondition
+        IllegalArgumentException.assertCondition(this.doGetFileState() === FileState.CLOSED, "File must be closed to open it.");
+
         // do something
     }
 
     public close(): void {
+        // precondition
+        IllegalArgumentException.assertCondition(this.doGetFileState() === FileState.OPEN, "File must be open to close it.");
+
         // do something
     }
 
diff --git a/src/adap-b04/files/Link.ts b/src/adap-b04/files/Link.ts
index e240325f..07e00430 100644
--- a/src/adap-b04/files/Link.ts
+++ b/src/adap-b04/files/Link.ts
@@ -1,11 +1,16 @@
 import { Node } from "./Node";
 import { Directory } from "./Directory";
+import { IllegalArgumentException } from "../common/IllegalArgumentException";
 
 export class Link extends Node {
 
     protected targetNode: Node | null = null;
 
     constructor(bn: string, pn: Directory, tn?: Node) {
+        // precondition
+        IllegalArgumentException.assertIsNotNullOrUndefined(pn);
+        IllegalArgumentException.assertCondition(typeof bn === "string" && bn.length > 0, "basename must be at least one character long.");
+
         super(bn, pn);
 
         if (tn != undefined) {
@@ -18,6 +23,9 @@ export class Link extends Node {
     }
 
     public setTargetNode(target: Node): void {
+        // precondition
+        IllegalArgumentException.assertIsNotNullOrUndefined(target);
+
         this.targetNode = target;
     }
 
@@ -27,12 +35,19 @@ export class Link extends Node {
     }
 
     public rename(bn: string): void {
+        // precondition
+        IllegalArgumentException.assertIsNotNullOrUndefined(bn);
+        IllegalArgumentException.assertCondition(typeof bn === "string" && bn.length > 0, "basename must be at least one character long.");
+
         const target = this.ensureTargetNode(this.targetNode);
         target.rename(bn);
     }
 
     protected ensureTargetNode(target: Node | null): Node {
-        const result: Node = this.targetNode as Node;
+        // precondition
+        IllegalArgumentException.assertIsNotNullOrUndefined(target);
+
+        const result: Node = target as Node;
         return result;
     }
 }
\ No newline at end of file
diff --git a/src/adap-b04/files/Node.ts b/src/adap-b04/files/Node.ts
index aa09c999..80cbfdae 100644
--- a/src/adap-b04/files/Node.ts
+++ b/src/adap-b04/files/Node.ts
@@ -1,3 +1,4 @@
+import { IllegalArgumentException } from "../common/IllegalArgumentException";
 import { Name } from "../names/Name";
 import { Directory } from "./Directory";
 
@@ -7,11 +8,18 @@ export class Node {
     protected parentNode: Directory;
 
     constructor(bn: string, pn: Directory) {
+        // precondition
+        IllegalArgumentException.assertIsNotNullOrUndefined(pn);
+        IllegalArgumentException.assertCondition(typeof bn === "string" && bn.length > 0, "basename must be at least one character long.");
+
         this.doSetBaseName(bn);
         this.parentNode = pn;
     }
 
     public move(to: Directory): void {
+        // precondition
+        IllegalArgumentException.assertIsNotNullOrUndefined(to);
+
         this.parentNode.remove(this);
         to.add(this);
     }
@@ -31,10 +39,16 @@ export class Node {
     }
 
     public rename(bn: string): void {
+        // precondition
+        IllegalArgumentException.assertCondition(typeof bn === "string" && bn.length > 0, "basename must be at least one character long.");
+
         this.doSetBaseName(bn);
     }
 
     protected doSetBaseName(bn: string): void {
+        // precondition
+        IllegalArgumentException.assertCondition(typeof bn === "string" && bn.length > 0, "basename must be at least one character long.");
+        
         this.baseName = bn;
     }
 
diff --git a/src/adap-b04/files/RootNode.ts b/src/adap-b04/files/RootNode.ts
index cff22b8d..104828d3 100644
--- a/src/adap-b04/files/RootNode.ts
+++ b/src/adap-b04/files/RootNode.ts
@@ -1,3 +1,4 @@
+import { IllegalArgumentException } from "../common/IllegalArgumentException";
 import { Name } from "../names/Name";
 import { StringName } from "../names/StringName";
 import { Directory } from "./Directory";
@@ -20,10 +21,16 @@ export class RootNode extends Directory {
     }
 
     public move(to: Directory): void {
+        // precondition
+        IllegalArgumentException.assertIsNotNullOrUndefined(to);
+
         // null operation
     }
 
     protected doSetBaseName(bn: string): void {
+        // precondition
+        IllegalArgumentException.assertCondition(typeof bn === "string" && bn.length > 0, "basename must be at least one character long.");
+
         // null operation
     }