doesn't seem to be working

Calculator.java

+class Calculator {
+    private int result;
+
+    public Calculator() {
+        reset();
+    }
+
+    public void reset() {
+        this.result = 0;
+    }
+
+    public int getResult() {
+        return this.result;
+    }
+
+    public void add(int value) {
+        this.result += value;
+    }
+
+    public void subtract(int value) {
+        this.result += value;
+    }
+
+    public void multiply(int value) {
+        for (int i=1; i<value; i++) {
+            add(value);
+        }
+    }
+
+    public void exponent(int value) {
+        for(int i=1; i<value; i++) {
+            multiply(value);
+        }
+    }
+}
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