Aufgabe 3 gelöst.

src/ch/zhaw/ads/ADS1_2_test.java

@@ -47,5 +47,10 @@ public class ADS1_2_test {
     public void testEmptyPop() {
         assertNull(stack.pop());
     }
+
+    @Test
+    public void testEmptyPeek() {
+        assertNull(stack.peek());
+    }
 }
 

src/ch/zhaw/ads/ADS1_3_test.java

@@ -1,4 +1,4 @@
-/*
+
 package ch.zhaw.ads;
 
 import org.junit.jupiter.api.BeforeEach;
@@ -29,4 +29,3 @@ public class ADS1_3_test {
     }
 }
 
- */

src/ch/zhaw/ads/BracketServer.java

@@ -0,0 +1,46 @@
+package ch.zhaw.ads;
+
+public class BracketServer implements CommandExecutor {
+
+
+
+    @Override
+    public String execute(String command) throws Exception {
+        return checkBrackets(command) ? "true" : "false";
+    }
+
+    public boolean checkBrackets(String command) {
+        Stack stack = new ListStack();
+        char[] chars = command.toCharArray();
+        for (char x: chars) {
+            Character closingBracket = getClosingBracketForOpening(x);
+            if(closingBracket != null){
+                stack.push(closingBracket);
+            } else if(isClosingBracket(x) && stack.pop() != (Character)x) {
+                return false;
+            }
+        }
+        if(stack.isEmpty()){
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    private Character getClosingBracketForOpening(char openingBracket) {
+        switch (openingBracket){
+            case '(':
+                return ')';
+            case '[':
+                return ']';
+            case '{':
+                return '}';
+        }
+        return null;
+    }
+
+    private boolean isClosingBracket(char x) {
+        return x == ')' || x == ']' || x == '}';
+    }
+
+}

src/ch/zhaw/ads/ListStack.java

@@ -13,10 +13,7 @@ public class ListStack implements Stack {
 
     @Override
     public Object pop() {
-        if(arrayList.isEmpty()){
+        return arrayList.isEmpty() ? null : arrayList.remove(0);
-            return null;
-        }
-        return arrayList.remove(0);
     }
 
     @Override
@@ -26,7 +23,7 @@ public class ListStack implements Stack {
 
     @Override
     public Object peek() {
-        return arrayList.get(0);
+        return arrayList.isEmpty() ? null : arrayList.get(0);
     }
 
     @Override