Update 0150.逆波兰表达式求值 Java Version

Add Java Solution with SwitchCase Approach

添加 Java 代码 Switch Case。更简洁一些。思路一样 都是 Stack

Author: Justin8584

problems/0150.逆波兰表达式求值.md

@@ -162,6 +162,40 @@ class Solution {
 }
 ```
 
+```Java
+// Switch Case 写法，更简洁一些
+class Solution {
+    public int evalRPN(String[] tokens) {
+        Stack<Integer> stk = new Stack<>();
+        for (String token : tokens) {
+
+            // 运算符Operator + - * /
+            if ("+-*/".contains(token)) {
+                int a = stk.pop()；
+		int b = stk.pop();
+                switch (token) {
+                    case "+":
+                        stk.push(a + b);
+                        break;
+                    case "-":
+                        stk.push(b - a);
+                        break;
+                    case "*":
+                        stk.push(a * b);
+                        break;
+                    case "/":
+                        stk.push(b / a);
+                        break;
+                }
+            } else {
+                stk.push(Integer.parseInt(token));
+            }
+        }
+        return stk.pop();
+    }
+}
+```
+
 ### Python3：
 
 ```python