adding java solution to problem 342. Power of Four

Author: hridoy100

java/342-Power-of-Four.java

@@ -0,0 +1,6 @@
+class Solution {
+    public boolean isPowerOfFour(int n) {
+        double x = Math.log(n)/Math.log(4);
+        return x==(int)x;
+    }
+}