实现 Stack

lzdragonix · lzdragonix · commit 3c5c6f143d52 · 2017-02-26T17:45:07.000+08:00
diff --git a/group04/24658892/learnjava/src/main/java/com/coding/basic/Stack.java b/group04/24658892/learnjava/src/main/java/com/coding/basic/Stack.java
@@ -1,22 +1,36 @@
 package com.coding.basic;
 
+import java.util.EmptyStackException;
+
 public class Stack {
-	private ArrayList elementData = new ArrayList();
-	
-	public void push(Object o){		
-	}
-	
-	public Object pop(){
-		return null;
-	}
-	
-	public Object peek(){
-		return null;
-	}
-	public boolean isEmpty(){
-		return false;
-	}
-	public int size(){
-		return -1;
-	}
+
+    private ArrayList elementData = new ArrayList();
+    private int size = 0;
+
+    public void push(Object o) {
+        elementData.add(o);
+        size++;
+    }
+
+    public Object pop() {
+        if (isEmpty()) {
+            throw new EmptyStackException();
+        }
+        return elementData.remove(--size);
+    }
+
+    public Object peek() {
+        if (this.isEmpty()) {
+            throw new EmptyStackException();
+        }
+        return elementData.get(size - 1);
+    }
+
+    public boolean isEmpty() {
+        return size == 0;
+    }
+
+    public int size() {
+        return size;
+    }
 }
