Update 0509.斐波那契数.md

增加java非压缩状态版本，易于理解

problems/0509.斐波那契数.md

@@ -186,6 +186,26 @@ class Solution {
 }
 ```
 
+```java
+//非压缩状态的版本
+class Solution {
+    public int fib(int n) {
+        if (n <= 1) return n;
+                
+        int[] dp = new int[n + 1];
+
+        dp[0] = 0;
+        dp[1] = 1;
+        
+        for (int index = 2; index <= n; index++){
+            dp[index] = dp[index - 1] + dp[index - 2];
+        }
+
+        return dp[n];
+    }
+}
+```
+
 Python：
 ```python3
 class Solution: