feat: add lab7

Lab7/cs2030s/fp/Constant.java

@@ -0,0 +1,18 @@
+package cs2030s.fp;
+
+/**
+ * Represent a function to initialise a constant value.
+ * CS2030S Lab 5
+ * AY22/23 Semester 1
+ *
+ * @param <T> The type of the constant value.
+ */
+@FunctionalInterface
+public interface Constant<T> {
+  /**
+   * The functional method to initialise the constant.
+   *
+   * @return The constant value.
+   */
+  T init();
+}