添加0020.有效的括号 Java版本

problems/0020.有效的括号.md

@@ -138,7 +138,31 @@ public:
 
 
 Java：
-
+```Java
+class Solution {
+    public boolean isValid(String s) {
+        Deque<Character> deque = new LinkedList<>();
+        char ch;
+        for (int i = 0; i < s.length(); i++) {
+            ch = s.charAt(i);
+            //碰到左括号，就把相应的右括号入栈
+            if (ch == '(') {
+                deque.push(')');
+            }else if (ch == '{') {
+                deque.push('}');
+            }else if (ch == '[') {
+                deque.push(']');
+            } else if (deque.isEmpty() || deque.peek() != ch) {
+                return false;
+            }else {//如果是右括号判断是否和栈顶元素匹配
+                deque.pop();
+            }
+        }
+        //最后判断栈中元素是否匹配
+        return deque.isEmpty();
+    }
+}
+```
 
 Python：
 ```python3