docs: adding subject and main

subjects/java/checkpoints/steady-sequence/ExerciseRunner.java

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+public class ExerciseRunner {
+    public static void main(String[] args) {
+        SteadySequence finder = new SteadySequence();
+
+        // Test case 1
+        int[] nums1 = {100, 4, 200, 1, 3, 2};
+        System.out.println("Longest consecutive sequence length: " + finder.longestSequence(nums1)); // Expected output: 4
+
+        // Test case 2
+        int[] nums2 = {0, 3, 7, 2, 5, 8, 4, 6, 0, 1};
+        System.out.println("Longest consecutive sequence length: " + finder.longestSequence(nums2)); // Expected output: 9
+
+        // Test case 3
+        int[] nums3 = {1, 2, 0, 1};
+        System.out.println("Longest consecutive sequence length: " + finder.longestSequence(nums3)); // Expected output: 3
+    }
+}

subjects/java/checkpoints/steady-sequence/README.md

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+## Steady Sequence
+
+### Instructions
+
+Create a class `SteadySequence` that provides a method to find the length of the longest consecutive elements sequence in an unsorted array of integers.
+
+### Expected Class
+
+```java
+import java.util.HashSet;
+import java.util.Set;
+
+public class SteadySequence {
+    public int longestSequence(int[] nums) {
+        // Implementation to find the length of the longest consecutive elements sequence
+    }
+}
+```
+
+### Usage
+
+Here is a possible `ExerciseRunner.java` to test your class:
+
+```java
+public class ExerciseRunner {
+    public static void main(String[] args) {
+        SteadySequence finder = new SteadySequence();
+
+        // Test case 1
+        int[] nums1 = {100, 4, 200, 1, 3, 2};
+        System.out.println("Longest consecutive sequence length: " + finder.longestSequence(nums1)); // Expected output: 4
+
+        // Test case 2
+        int[] nums2 = {0, 3, 7, 2, 5, 8, 4, 6, 0, 1};
+        System.out.println("Longest consecutive sequence length: " + finder.longestSequence(nums2)); // Expected output: 9
+
+        // Test case 3
+        int[] nums3 = {1, 2, 0, 1};
+        System.out.println("Longest consecutive sequence length: " + finder.longestSequence(nums3)); // Expected output: 3
+    }
+}
+```
+
+### Expected Output
+
+```shell
+$ javac *.java -d build
+$ java -cp build ExerciseRunner
+Longest consecutive sequence length: 4
+Longest consecutive sequence length: 9
+Longest consecutive sequence length: 3
+$
+```