diff --git a/2D_Array/readme.md b/2D_Array/readme.md
index 74f031c3a..5aa604c3f 100644
--- a/2D_Array/readme.md
+++ b/2D_Array/readme.md
@@ -13,6 +13,7 @@ Due to the fact that the elements of 2D arrays can be random accessed. Similar t
 * Checking Teoplitz Matrix Algorithm ----> [Java](/Code/Java/Toeplitz.java)
 * Clockwise Rotation ----> [C++](/Code/C++/2d_matrix_rotation_90degree_clockwise.cpp)
 * Inverse of a Matrix ----> [Java](/Code/Java/matrixop_inverse.java)
+* Longest Substring Without Repeating Characters ----> [Java](/Code/Java/Longest_Substring.java) 
 * Matrix Operations ----> [C++](/Code/C++/matrix_operations.cpp)
 * Multiplication of two Matrices ----> [Java](/Code/Java/matrixop_mul.java)
 * Overall Median of Matrix ---> [Java](/Code/Java/overall_median_matrix.java)
@@ -20,5 +21,5 @@ Due to the fact that the elements of 2D arrays can be random accessed. Similar t
 * Spiral Print ----> [C++](/Code/C++/spiral_print.cpp)
 * Staircase Search ----> [C++](/Code/C++/staircase_search.cpp)
 * Substraction of two Matrices ----> [Java](/Code/Java/matrixop_sub.java)
-* Transpose of a Matrix --->[Java](/Code/Java/transpose.java) | [Python](/Code/Python/Transpose_of_matrix.py)
+* Transpose of a Matrix --->[Java](/Code/Java/transpose.java) | [](/Code//Transpose_of_matrix.py)
 * Wave Print ----> [C++](/Code/C++/wave_print.cpp)
diff --git a/Code/Java/Longest_Substring.java b/Code/Java/Longest_Substring.java
new file mode 100644
index 000000000..1235661ff
--- /dev/null
+++ b/Code/Java/Longest_Substring.java
@@ -0,0 +1,47 @@
+// Question 
+
+// Given a string s, find the length of the longest substring without repeating characters.
+
+// Example 1:
+
+// Input: s = "abcabcbb"
+// Output: 3
+// Explanation: The answer is "abc", with the length of 3.
+// Example 2:
+
+// Input: s = "bbbbb"
+// Output: 1
+// Explanation: The answer is "b", with the length of 1.
+// Example 3:
+
+// Input: s = "pwwkew"
+// Output: 3
+// Explanation: The answer is "wke", with the length of 3.
+// Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.
+// Example 4:
+
+// Input: s = ""
+// Output: 0 
+
+// *****************************************************************************************************
+
+
+// Solution
+
+public class Longest Substring {
+    public int lengthOfLongestSubstring(String s) {
+        int len = s.length();
+        int ans=0;
+        Map<Character,Integer> map = new HashMap<>();
+        for(int j=0, i=0; j<len; j++){
+            if(map.containsKey(s.charAt(j)))
+                i = .max(map.get(s.charAt(j)), i);
+            ans = .max(ans, j-i+1);
+            map.put(s.charAt(j), j+1);
+        }
+        return ans;
+    }   
+}
+
+// Time Complexity = O(n)
+// Space Complexity = O(n)