add Stream related solutions

ImamBiplob · ImamBiplob · commit caebf8648a3b · 2023-08-20T15:09:51.000+06:00
diff --git a/More Core Java Concepts to Know/CreatingStreams/CreatingStreams.java b/More Core Java Concepts to Know/CreatingStreams/CreatingStreams.java
@@ -0,0 +1,24 @@
+package CreatingStreams;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class CreatingStreams {
+    public static void main(String[] args) {
+        // A stream consists of a source followed by zero or more intermediate methods combined together(pipelined) and
+        // a terminal method to process the objects obtained from the source as per the methods described.
+        // Stream is used to compute elements as per the pipelined methods without altering the original value of the object.
+
+        Stream<Integer> stream = Stream.of(1,2,3,4,5);  // Stream using Stream.of()
+        stream.forEach(System.out::println);
+
+        int []arr = {2,4,8,16};
+        int sum = Arrays.stream(arr).sum();  // Stream from array
+        System.out.println(sum);
+
+        List<Integer> numbers = Arrays.asList(1,3,5,7);
+        numbers.stream().map(i -> i+1).collect(Collectors.toList()).forEach(System.out::println);  // Stream from collection
+    }
+}
diff --git a/More Core Java Concepts to Know/ExceptionHandlingBestPractices/ListOfBestPractices.java b/More Core Java Concepts to Know/ExceptionHandlingBestPractices/ListOfBestPractices.java
@@ -0,0 +1,12 @@
+package ExceptionHandlingBestPractices;
+
+public class ListOfBestPractices {
+    // Use specific exception classes for different types of errors
+    // Catch exceptions at the appropriate level of abstraction
+    // Log and handle exceptions in a consistent and informative manner
+    // Avoid empty catch blocks and swallowing exceptions
+    // Propagate exceptions up the call stack when appropriate
+    // Use finally blocks for cleanup and resource management
+    // Use a global exception handler
+    // Don’t close resources manually
+}
diff --git a/More Core Java Concepts to Know/FunctionalInterfacesInJDK/FuncInterfacesDemo.java b/More Core Java Concepts to Know/FunctionalInterfacesInJDK/FuncInterfacesDemo.java
@@ -29,4 +29,4 @@ public static void main(String[] args) {
         System.out.println(supplier.get());
 
     }
-}
+}
diff --git a/More Core Java Concepts to Know/InfiniteStreams/InfiniteStreams.java b/More Core Java Concepts to Know/InfiniteStreams/InfiniteStreams.java
@@ -0,0 +1,15 @@
+package InfiniteStreams;
+
+import java.util.Random;
+import java.util.stream.IntStream;
+
+public class InfiniteStreams {
+    public static void main(String[] args) {
+        IntStream
+                .iterate(0, i -> i+1)
+                .forEach(System.out::println);
+
+        Random random = new Random();
+        IntStream.generate(random::nextInt).forEach(System.out::println);
+    }
+}
diff --git a/More Core Java Concepts to Know/StreamAPIForFilteringAndTransformation/FilteringAndTransformation.java b/More Core Java Concepts to Know/StreamAPIForFilteringAndTransformation/FilteringAndTransformation.java
@@ -0,0 +1,19 @@
+package StreamAPIForFilteringAndTransformation;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class FilteringAndTransformation {
+    public static void main(String[] args) {
+        List<Integer> numbers = new ArrayList<>();
+        numbers.add(1);
+        numbers.add(2);
+        numbers.add(3);
+        numbers.add(4);
+        numbers.add(5);
+
+        List evenNumbers = numbers.stream().filter(e -> e % 2 == 0).map(e -> e*e).collect(Collectors.toList());
+        System.out.println(evenNumbers);
+    }
+}
diff --git a/More Core Java Concepts to Know/StreamAPIForGroupingAndAggregation/Employee.java b/More Core Java Concepts to Know/StreamAPIForGroupingAndAggregation/Employee.java
@@ -0,0 +1,27 @@
+package StreamAPIForGroupingAndAggregation;
+
+public class Employee {
+
+    private String name;
+    private String department;
+    private double salary;
+
+    public Employee(String name, String department, double salary) {
+        this.name = name;
+        this.department = department;
+        this.salary = salary;
+    }
+
+    public String getDepartment() {
+        return department;
+    }
+
+    public double getSalary() {
+        return salary;
+    }
+
+    @Override
+    public String toString() {
+        return name;
+    }
+}
diff --git a/More Core Java Concepts to Know/StreamAPIForGroupingAndAggregation/GroupingAndAggregation.java b/More Core Java Concepts to Know/StreamAPIForGroupingAndAggregation/GroupingAndAggregation.java
@@ -0,0 +1,23 @@
+package StreamAPIForGroupingAndAggregation;
+
+import java.util.ArrayList;
+import java.util.DoubleSummaryStatistics;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class GroupingAndAggregation {
+    public static void main(String[] args) {
+        List<Employee> employees = new ArrayList<>();
+        employees.add(new Employee("Imam", "Technical", 10000));
+        employees.add(new Employee("Biplob", "HR", 9000));
+        employees.add(new Employee("Rakib", "Technical", 8000));
+
+        var groupedEmployees = employees.stream()
+                .collect(Collectors.groupingBy(Employee::getDepartment,
+                                                Collectors.averagingDouble(Employee::getSalary)));
+        System.out.println(groupedEmployees);   // Average salary for all departments
+
+        DoubleSummaryStatistics summary = employees.stream().mapToDouble(Employee::getSalary).summaryStatistics();
+        System.out.println(summary.getAverage());  // Average salary for all employees
+    }
+}
diff --git a/More Core Java Concepts to Know/StreamIntermediateAndTerminalOps/StreamOps.java b/More Core Java Concepts to Know/StreamIntermediateAndTerminalOps/StreamOps.java
@@ -0,0 +1,31 @@
+package StreamIntermediateAndTerminalOps;
+
+import StreamAPIForGroupingAndAggregation.Employee;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class StreamOps {
+    public static void main(String[] args) {
+        List<Integer> numbers = Arrays.asList(64,1,2,4,8,16,32);
+        int sumOfFilteredNumbers = numbers.stream()
+                .filter(n -> n%4==0)
+                .map(n -> n*n)
+                .reduce(0,(sum,i) -> sum+i);
+        System.out.println(sumOfFilteredNumbers);
+
+        numbers.stream()
+                .sorted()
+                .collect(Collectors.toList())
+                .forEach(System.out::println);
+
+        List<Employee> employees = List.of(new Employee("Imam", "Technical", 10000),
+                new Employee("Biplob", "HR", 9000),
+                new Employee("Rakib", "Technical", 8000));
+        employees.stream()
+                .sorted(Comparator.comparing(Employee::getSalary))
+                .forEach(System.out::println);
+    }
+}

Original file line number	Diff line number	Diff line change
`@@ -29,4 +29,4 @@ public static void main(String[] args) {`
`29`	`29`	`System.out.println(supplier.get());`
`30`	`30`
`31`	`31`	`}`
`32`		`-}`
	`32`	`+}`