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<\/a><\/figure>\n<\/div>\nBefore diving deep into the practice stuff let us understand the methods we will be covering in this tutorial.<\/p>\n
- \n
- The
distinct()<\/code> method returns a stream of unique elements. It is a stateful intermediate operation and returns a new stream. This method useshashCode()<\/code> andequals()<\/code> to get the unique elements<\/li>\n- The
sorted()<\/code> method returns a stream consisting of elements in the sorted natural order. This method can also accept a comparator to provide customized sorting. It is a stateful intermediate operation and returns a new stream<\/li>\n- The
count()<\/code> method returns the count of elements in a stream<\/li>\n<\/ul>\n2. Practice<\/h2>\n
Let us dive into some practice stuff from here and I am assuming that you already have the Java 1.8 or greater installed in your local machine. I am using JetBrains IntelliJ IDEA<\/a> as my preferred IDE. You’re free to choose the IDE of your choice.<\/p>\n
2.1 Model class<\/h3>\n
Create a java file in the
com.java8.util<\/code> package and add the following code. The class will act as a model class for the creation of the employee list.<\/p>\nEmployee.java<\/em><\/span><\/p>\n
package com.java8.util;\n\nimport java.util.ArrayList;\nimport java.util.List;\n\npublic class Employee {\n private final String email;\n private final int age;\n\n private Employee(String email, int age) {\n this.email = email;\n this.age = age;\n }\n\n public static List<Employee> create() {\n List<Employee> employees = new ArrayList<>();\n employees.add(new Employee(\"john@email.com\", 21));\n employees.add(new Employee(\"martin@email.com\", 19));\n employees.add(new Employee(\"marry@email.com\", 31));\n employees.add(new Employee(\"john@email.com\", 27));\n employees.add(new Employee(\"marry@email.com\", 25));\n\n return employees;\n }\n\n public String getEmail() {\n return email;\n }\n\n public int getAge() {\n return age;\n }\n\n @Override\n public String toString() {\n return \"Employee [email=\" + email + \", age=\" + age + \"]\";\n }\n}\n<\/pre>\n2.2 Understanding distinct() method<\/h3>\n
Create a java file in the
com.java8<\/code> package and add the following code. The class will show thedistinct()<\/code> method implementation in different ways.<\/p>\nDistinctDemo.java<\/em><\/span><\/p>\n
package com.java8;\n\nimport com.java8.util.Employee;\n\nimport java.util.Arrays;\nimport java.util.List;\nimport java.util.Set;\nimport java.util.concurrent.ConcurrentHashMap;\nimport java.util.function.Function;\nimport java.util.function.Predicate;\nimport java.util.stream.Collectors;\n\npublic class DistinctDemo {\n\n \/\/ distinct() method returns a stream of unique elements\n \/\/ uses the hashCode() and equals() method to get the unique elements\n\n \/\/ removing duplicates from primitive type\n private static void method1() {\n List<Integer> duplicates = Arrays.asList(1, 2, 2, 3, 4, 5, 6, 6, 1, 8, 0, 10);\n print(\"Original list: \", duplicates);\n\n List<Integer> unique = duplicates.stream()\n .distinct()\n .collect(Collectors.toList());\n print(\"Distinct list: \", unique);\n }\n\n\n \/\/ removing duplicates from object\n private static void method2() {\n List<Employee> employees = Employee.create();\n print(\"Original list: \", employees);\n\n List<Employee> distinct = employees.stream()\n .filter(distinctByKey(Employee::getEmail)) \/\/ using the predicate to remove the duplicated\n .collect(Collectors.toList());\n print(\"Distinct list: \", distinct);\n }\n\n \/\/ predicate to filter the duplicates by the given key extractor\n \/\/ does the job to remove the duplicates\n private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {\n Set<Object> seen = ConcurrentHashMap.newKeySet();\n return t -> seen.add(keyExtractor.apply(t));\n }\n\n \/\/ print the list\n private static void print(String message, List<?> some) {\n System.out.println(message + some);\n }\n\n \/\/ driver code\n public static void main(String[] args) {\n System.out.println(\"-- Streams distinct() method --\\n\");\n\n method1();\n\n System.out.println(\"\\n\");\n\n method2();\n }\n}\n<\/pre>\nRun the file as a java application and if everything goes well the following output will be logged in the IDE console.
<\/div> <\/div><\/p>\nConsole output<\/em><\/span><\/p>\n
-- Streams distinct() method --\n\nOriginal list: [1, 2, 2, 3, 4, 5, 6, 6, 1, 8, 0, 10]\nDistinct list: [1, 2, 3, 4, 5, 6, 8, 0, 10]\n\n\nOriginal list: [Employee [email=john@email.com, age=21], Employee [email=martin@email.com, age=19], Employee [email=marry@email.com, age=31], Employee [email=john@email.com, age=27], Employee [email=marry@email.com, age=25]]\nDistinct list: [Employee [email=john@email.com, age=21], Employee [email=martin@email.com, age=19], Employee [email=marry@email.com, age=31]]\n<\/pre>\n
2.3 Understanding count() method<\/h3>\n
Create a java file in the
com.java8<\/code> package and add the following code. The class will show thecount()<\/code> method implementation in different ways.<\/p>\nCountDemo.java<\/em><\/span><\/p>\n
package com.java8;\n\nimport com.java8.util.Employee;\n\nimport java.util.Arrays;\nimport java.util.List;\n\npublic class CountDemo {\n\n \/\/ count() method counts the number of elements in the stream\n\n private static void method1() {\n List<Integer> list = Arrays.asList(1, 2, 2, 3, 4, 5, 6, 6, 1, 8, 0, 10);\n\n long total = list.stream()\n .count();\n System.out.println(\"Total elements = \" + total);\n }\n\n private static void method2() {\n List<Employee> employees = Employee.create();\n\n long total = employees.stream().count();\n System.out.println(\"Total employees = \" + total);\n\n long freshers = employees.stream()\n .filter(employee -> employee.getAge() <= 21)\n .count();\n System.out.println(\"Total employees after filter(..) op = \" + freshers);\n }\n\n \/\/ driver code\n public static void main(String[] args) {\n System.out.println(\"-- Streams count() method --\\n\");\n\n method1();\n\n System.out.println(\"\\n\");\n\n method2();\n }\n}\n<\/pre>\nRun the file as a java application and if everything goes well the following output will be logged in the IDE console.[ulp id=’mp4qw6feirku6wM7′ name=’Java 8 Features Inline’]<\/p>\n
Console output<\/em><\/span><\/p>\n
-- Streams count() method --\n\nTotal elements = 12\n\n\nTotal employees = 5\nTotal employees after filter(..) op = 2\n<\/pre>\n
2.4 Understanding sorted() method<\/h3>\n
Create a java file in the
com.java8<\/code> package and add the following code. The class will show thesorted()<\/code> method implementation in different ways.<\/p>\nSortedDemo.java<\/em><\/span><\/p>\n
package com.java8;\n\nimport com.java8.util.Employee;\n\nimport java.util.Arrays;\nimport java.util.Comparator;\nimport java.util.List;\nimport java.util.stream.Collectors;\n\npublic class SortedDemo {\n\n\t\/\/ sorted() method returns a stream consisting of elements in a sorted order\n\t\/\/ it is a stateful intermediate operation\n\n\t\/\/ sorting primitive type list\n\tprivate static void method1() {\n\t\tList<Integer> unsorted = Arrays.asList(1, 2, 2, 3, 4, 5, 6, 6, 1, 8, 0, 10);\n\t\tSystem.out.println(\"Unsorted stream:\" + unsorted);\n\n\t\tList<Integer> sorted = unsorted.stream()\n\t\t\t\t.sorted()\n\t\t\t\t.collect(Collectors.toList());\n\t\tSystem.out.println(\"Sorted stream:\" + sorted);\n\t}\n\n\t\/\/ sorting object list\n\tprivate static void method2() {\n\t\tList<Employee> employees = Employee.create();\n\n\t\tList<Employee> sorted = employees.stream()\n\t\t\t\t.sorted(Comparator.comparing(Employee::getAge)) \/\/ sorting the employees by age\n\t\t\t\t.collect(Collectors.toList());\n\t\tSystem.out.println(\"Sorted list : \" + sorted);\n\t}\n\n\t\/\/ driver code\n\tpublic static void main(String[] args) {\n\t\tSystem.out.println(\"-- Streams sorted() method --\\n\");\n\n\t\tmethod1();\n\n\t\tSystem.out.println(\"\\n\");\n\n\t\tmethod2();\n\t}\n}\n<\/pre>\nRun the file as a java application and if everything goes well the following output will be logged in the IDE console.<\/p>\n
Console output<\/em><\/span><\/p>\n
-- Streams sorted() method --\n\nUnsorted stream:[1, 2, 2, 3, 4, 5, 6, 6, 1, 8, 0, 10]\nSorted stream:[0, 1, 1, 2, 2, 3, 4, 5, 6, 6, 8, 10]\n\n\nSorted list : [Employee [email=martin@email.com, age=19], Employee [email=john@email.com, age=21], Employee [email=marry@email.com, age=25], Employee [email=john@email.com, age=27], Employee [email=marry@email.com, age=31]]\n<\/pre>\n
That is all for this tutorial and I hope the article served you with whatever you were looking for. Happy Learning and do not forget to share!<\/p>\n
4. Summary<\/h2>\n
In this tutorial, we learned the
sorted()<\/code>,count()<\/code>, anddistinct()<\/code> methods introduced in java8 programming along with the implementation. You can download the source code from the Downloads<\/a> section.<\/p>\n<\/a>5. Download the Project<\/h2>\n
This was a tutorial on learning and implementing the
sorted()<\/code>,count()<\/code>, anddistinct()<\/code> methods in Java 8.<\/p>\n - The