add Rule13

yi-yun · yi-yun · commit 38d00035f8a1 · 2019-06-30T17:28:23.000+08:00
diff --git a/effective_java/src/main/java/com/yiyun/Rule13/StackClone.java b/effective_java/src/main/java/com/yiyun/Rule13/StackClone.java
@@ -0,0 +1,38 @@
+package com.yiyun.Rule13;
+
+import java.util.Arrays;
+import java.util.EmptyStackException;
+
+public class StackClone implements Cloneable{
+    private Object[] elements;
+    private int size = 0;
+    private static final int DEFAULT_INITIAL_CAPACITY = 16;
+
+    public StackClone() {
+        this.elements = new Object[DEFAULT_INITIAL_CAPACITY];
+    }
+
+    @Override
+    protected StackClone clone() throws CloneNotSupportedException {
+        return (StackClone)super.clone();
+    }
+
+    public void push(Object e) {
+        ensureCapacity();
+        elements[size++] = e;
+    }
+
+    public Object pop() {
+        if (size == 0)
+            throw new EmptyStackException();
+        Object result = elements[--size];
+        elements[size] = null; // Eliminate obsolete reference
+        return result;
+    }
+
+    // Ensure space for at least one more element.
+    private void ensureCapacity() {
+        if (elements.length == size)
+            elements = Arrays.copyOf(elements, 2 * size + 1);
+    }
+}
diff --git a/effective_java/src/main/java/com/yiyun/Rule13/TestClone.java b/effective_java/src/main/java/com/yiyun/Rule13/TestClone.java
@@ -0,0 +1,13 @@
+package com.yiyun.Rule13;
+
+import com.yiyun.Rule07.MyStack;
+
+public class TestClone {
+    public static void main(String[] args) throws Exception{
+        StackClone stackClone = new StackClone();
+        StackClone clone = stackClone.clone();
+        for (int i = 0; i < 18; i++) {
+            stackClone.push(i);
+        }
+    }
+}
