Java 8 Function Examples (apply() and Chain Methods andThen(), identity())

Author: java-w3schools

pom.xml

@@ -19,6 +19,13 @@
             <type>pom</type>
             <scope>provided</scope>
         </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-log4j12</artifactId>
+            <version>1.7.30</version>
+        </dependency>
+
+
     </dependencies>
     <build>
         <finalName>corejav</finalName>

src/main/java/com/airhacks/JAXRSConfiguration.java

@@ -0,0 +1,25 @@
+package com.javaprogramto.java8.functional.interfaces.function;
+
+import com.javaprogramto.models.Employee;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Function;
+
+public class EmployeeFuntionEample {
+
+    public static void main(String[] args) {
+
+        Function<Employee, String> empString = employee -> employee.getAge() + " - " + employee.getFullName();
+
+        List<Employee> list = new ArrayList<Employee>();
+        list.add(new Employee(100, "Jhon Paul", 25));
+        list.add(new Employee(101, "Narmad Rao", 30));
+
+        for (Employee emp : list) {
+            String empInStr = empString.apply(emp);
+            System.out.println(empInStr);
+        }
+
+    }
+}

src/main/java/com/airhacks/ping/boundary/PingResource.java

@@ -0,0 +1,40 @@
+package com.javaprogramto.java8.functional.interfaces.function;
+
+import com.javaprogramto.models.Employee;
+import org.apache.log4j.BasicConfigurator;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+
+public class FunctionListToMap {
+
+  static Logger logger = LoggerFactory.getLogger(FunctionListToMap.class);
+
+    public static void main(String[] args) {
+        BasicConfigurator.configure();
+
+        // Createing a list
+        List<Employee> list = new ArrayList<Employee>();
+        list.add(new Employee(100, "Jhon Paul", 25));
+        list.add(new Employee(101, "Narmad Rao", 30));
+
+        // Creating Function to convert List to Map.
+        Function<List<Employee>, Map<Integer, Employee>> listToMap = employees -> {
+
+            Map<Integer, Employee> newMap = new HashMap<>();
+            for (Employee e : employees
+            ) {
+                newMap.put(e.getId(), e);
+            }
+            return newMap;
+        };
+
+        Map<Integer, Employee> empMap = listToMap.apply(list);
+        logger.info("List to Map : " + empMap);
+    }
+}

src/main/java/com/javaprogramto/java8/functional/interfaces/function/EmployeeFuntionEample.java

@@ -0,0 +1,34 @@
+package com.javaprogramto.java8.functional.interfaces.function;
+
+import com.javaprogramto.models.Employee;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+public class FunctionMethodExamples {
+
+    public static void main(String[] args) {
+
+        Function<Employee, String> empToStringFunction = emp -> emp.getFullName();
+
+        Function<String, Integer> stringToIntFunction = str -> str.length();
+
+        Function<Integer, Integer> squereFunction = numner -> numner * numner;
+
+        // chain() method example
+        Integer squere = empToStringFunction.andThen(stringToIntFunction).andThen(squereFunction).apply(new Employee(500, "Lady Gaga", 50));
+
+        System.out.println("andThen() example to get Employee name length squere : " + squere);
+
+        // identity() example
+        String input = "aaaaa bbbbb";
+        Map chars = input.codePoints().mapToObj(cp -> cp)
+                .collect(Collectors.groupingBy(Function.identity(), LinkedHashMap::new, Collectors.counting()));
+
+        System.out.println("identity chars "+chars);
+    }
+
+
+}

src/main/java/com/javaprogramto/java8/functional/interfaces/function/FunctionListToMap.java

@@ -0,0 +1,19 @@
+package com.javaprogramto.java8.functional.interfaces.function;
+
+import java.util.function.Function;
+
+public class java8FunctionExample {
+
+    public static void main(String[] args) {
+
+        Function<String, Integer> function = str -> str.length();
+
+        int length = function.apply("Hello world");
+        System.out.println("Fucntion to find string length :" + length);
+
+        Function<Integer, String> function2 = number -> String.valueOf(number) + " is now String";
+
+        String output = function2.apply(1260);
+        System.out.println("Funtion to covnert Integer to String : "+output);
+    }
+}

src/main/java/com/javaprogramto/java8/functional/interfaces/function/FunctionMethodExamples.java

@@ -0,0 +1,47 @@
+package com.javaprogramto.models;
+
+public class Employee {
+
+    private int id;
+    private String fullName;
+    private int age;
+
+    public Employee(int id, String fullName, int age) {
+        this.id = id;
+        this.fullName = fullName;
+        this.age = age;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getFullName() {
+        return fullName;
+    }
+
+    public void setFullName(String fullName) {
+        this.fullName = fullName;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    @Override
+    public String toString() {
+        return "Employee{" +
+                "id=" + id +
+                ", fullName='" + fullName + '\'' +
+                ", age=" + age +
+                '}';
+    }
+}

src/main/java/com/javaprogramto/java8/functional/interfaces/function/java8FunctionExample.java

@@ -8,16 +8,17 @@ public static void main(String[] args) {
 		int secondNumber = 20;
 
 
-		System.out
-				.println("Before swapping two numbers : firstNumber " + firstNumber + ", secondNumber " + secondNumber);
+		System.out.println("Before swapping two numbers : firstNumber "
+		+ firstNumber + ", secondNumber " + secondNumber);
+		
 
 
 		firstNumber = firstNumber + secondNumber;
 		secondNumber = firstNumber - secondNumber;
 		firstNumber = firstNumber - secondNumber;
 
 
-		System.out
-				.println("After swapping two numbers : firstNumber " + firstNumber + ", secondNumber " + secondNumber);
+		System.out.println("After swapping two numbers : firstNumber "
+		+ firstNumber + ", secondNumber " + secondNumber);
 	}
 }

src/main/java/com/javaprogramto/models/Employee.java

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/java" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>