Hacktoberfest contributions for JAVA

JAVA/FirstAndLastIndex.java

@@ -0,0 +1,15 @@
+import java.util.Scanner;
+public class FirstAndLastIndex 
+{ 
+    public static void main(String[] args) 
+    { 
+        try (Scanner sc = new Scanner(System.in)) {
+            System.out.println("Enter String:");
+            String str = sc.next(); 
+            System.out.println("Enter character or substring to search: ");
+            String substr = sc.next(); 
+            System.out.println("First occurence "+ str.indexOf(substr)); 
+            System.out.println("Last occurence "+ str.lastIndexOf(substr));
+        } 
+    } 
+}

JAVA/HashMaps.java

@@ -0,0 +1,39 @@
+import java.util.*;
+import java.util.Map.Entry; 
+
+class HashMaps { 
+
+    public static void main(String[] args) 
+    { 
+        HashMap<Integer, String> map = new HashMap<>(); 
+        map.put(1, "A"); 
+        map.put(2, "B"); 
+        map.put(3, "C"); 
+        map.put(4, "D"); 
+        map.put(5, "E"); 
+        if (map.containsKey(3)) { 
+            System.out.println("Key 3 is present with value: "+ map.get(3)); 
+        } 
+        else { 
+            System.out.println("Key 3 is not present"); 
+        } 
+        if (map.containsValue("A")) { 
+            System.out.println("Value A is present"); 
+        } 
+        else{
+            System.out.println("Value A is absent"); 
+        }
+
+	Set<Integer> keys = map.keySet(); 
+
+	for (Integer key : keys) 
+		System.out.println(key); 
+
+	Set<Entry<Integer, String>> entries 
+							= map.entrySet(); 
+
+	for (Entry<Integer, String> entry : entries) 
+		System.out.println(entry.getKey() + " : "
+						+ entry.getValue()); 
+} 
+} 

JAVA/HashSets.java

@@ -0,0 +1,40 @@
+import java.util.*;
+class HashSets{
+    public static void main(String[] args) {
+        Set <String> set= new HashSet<>();
+        set.add("a");
+        set.add("b");
+        set.add("c");
+        ArrayList<String> list= new ArrayList<String>();
+        list.add("x");
+        list.add("y");
+        list.add("z");
+        set.addAll(list);
+        Iterator<String> itr=set.iterator();
+        while(itr.hasNext() ){
+            System.out.println(itr.next());
+        }
+        set.clear();
+        System.out.println("Deleted all elements\nNew elements");
+
+        set.add("John");
+        set.add("David");
+        set.add("Mike");
+        set.add("Ricky");
+        Iterator<String> itr2=set.iterator();
+        while(itr2.hasNext() ){
+            System.out.println(itr2.next());
+        }
+        try (Scanner sc = new Scanner(System.in)) {
+            System.out.print("Enter name to search: ");
+            String name=sc.next();
+
+            if(set.contains(name))
+                System.out.println(name+" found in the list");
+            else
+                System.out.println(name+" not found in the list");
+        }
+    }
+}
+
+