Java Examples

Author: lokeshgupta1981

src/main/java/com/howtodoinjava/core/datatypes/Employee.java

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+package com.howtodoinjava.core.datatypes;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class Employee {
+
+  public static void main(String[] args) {
+    Stream<String> tokenStream = Stream.of("A", "B", "C", "D");
+    ArrayList<String> tokenList = tokenStream.collect(Collectors.toCollection(ArrayList::new));
+    tokenList.add("e");
+    System.out.println(tokenList);
+
+    List list = Arrays.asList("A", "B", "C");
+    list.add("e");
+    System.out.println(list);
+
+    ArrayList<String> arraylist = new ArrayList<>(Arrays.asList("A", "B", "C"));
+  }
+
+}
+
+

src/main/java/com/howtodoinjava/core/datetime/FirstAndLastDay.java

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+package com.howtodoinjava.core.datetime;
+
+import java.time.DayOfWeek;
+import java.time.LocalDate;
+import java.time.temporal.TemporalAdjusters;
+
+public class FirstAndLastDay {
+
+  public static void main(String[] args) {
+    LocalDate today = LocalDate.of(2024, 4, 26);
+
+    //Week
+    LocalDate firstDayOfWeek = today.with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY));
+    LocalDate lastDayOfWeek = today.with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY));
+
+    System.out.println(firstDayOfWeek);  //2024-04-22
+    System.out.println(lastDayOfWeek);  //2024-04-22
+
+    //Month
+    LocalDate firstDayOfMonth = today.withDayOfMonth(1);
+    LocalDate lastDayOfMonth = today.withDayOfMonth(today.lengthOfMonth());
+
+    System.out.println(firstDayOfMonth);  //2024-04-01
+    System.out.println(lastDayOfMonth);   //2024-04-30
+
+    firstDayOfMonth = today.with(TemporalAdjusters.firstDayOfMonth());
+    lastDayOfMonth = today.with(TemporalAdjusters.lastDayOfMonth());
+
+    System.out.println(firstDayOfMonth);  //2024-04-01
+    System.out.println(lastDayOfMonth);   //2024-04-30
+
+    //Year
+    LocalDate firstDayOfYear = today.with(TemporalAdjusters.firstDayOfYear());
+    LocalDate lastDayOfYear = today.with(TemporalAdjusters.lastDayOfYear());
+
+    System.out.println(firstDayOfYear);   //2024-01-01
+    System.out.println(lastDayOfYear);    //2024-12-31
+  }
+}

src/main/java/com/howtodoinjava/core/streams/MapMultiExample.java

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+package com.howtodoinjava.core.streams;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class MapMultiExample {
+
+  public static void main(String[] args) {
+
+    List<Integer> numbers = List.of(1, 2, 3);
+
+    List<Integer> multiples = numbers.stream().<Integer>mapMulti((num, downstream) -> {
+      downstream.accept(num);
+      downstream.accept(num * num); // Add the square of the number
+      downstream.accept(num * num * num); // Add the cube of the number
+    }).toList();
+
+    System.out.println(multiples); // Output: [2, 3, 4, 6, 6, 9, 8, 12, 10, 15]
+
+    // second example
+
+    // Sample list of transactions
+    List<Transaction> transactions = List.of(
+        new Transaction("T1", 100, TransactionType.DEPOSIT),
+        new Transaction("T2", 50, TransactionType.WITHDRAWAL),
+        new Transaction("T3", 200, TransactionType.WITHDRAWAL));
+
+    // Process transactions and generate transaction events
+    List<TransactionEvent> transactionEvents = transactions.stream()
+        .<TransactionEvent>mapMulti((transaction, downstream) -> {
+          if (transaction.getType() == TransactionType.DEPOSIT) {
+            downstream.accept(new TransactionEvent("Deposit", transaction.getAmount()));
+          } else if (transaction.getType() == TransactionType.WITHDRAWAL) {
+            downstream.accept(new TransactionEvent("Withdrawal", transaction.getAmount()));
+            // If withdrawal amount is greater than 100, generate an additional fraud alert event
+            if (transaction.getAmount() > 100) {
+              downstream.accept(new TransactionEvent("Fraud Alert", transaction.getAmount()));
+            }
+          }
+        }).toList();
+
+    // Print the generated transaction events
+    transactionEvents.forEach(System.out::println);
+  }
+
+  static class Transaction {
+
+    private String id;
+    private double amount;
+    private TransactionType type;
+
+    public Transaction(String id, double amount, TransactionType type) {
+      this.id = id;
+      this.amount = amount;
+      this.type = type;
+    }
+
+    public String getId() {
+      return id;
+    }
+
+    public double getAmount() {
+      return amount;
+    }
+
+    public TransactionType getType() {
+      return type;
+    }
+  }
+
+  static class TransactionEvent {
+
+    private String type;
+    private double amount;
+
+    public TransactionEvent(String type, double amount) {
+      this.type = type;
+      this.amount = amount;
+    }
+
+    @Override
+    public String toString() {
+      return "TransactionEvent{" + "type='" + type + '\'' + ", amount=" + amount + '}';
+    }
+  }
+
+  enum TransactionType {
+    DEPOSIT, WITHDRAWAL
+  }
+}