Bael 8067 (#16811)

* pass function as parameter"

* pass function as parameter

Author: wynnteo

core-java-modules/core-java-function/src/main/java/com/baeldung/functionparameter/FunctionParameter.java

@@ -0,0 +1,45 @@
+package com.baeldung.functionparameter;
+
+import java.util.function.BiFunction;
+import java.util.concurrent.Callable;
+
+interface Operation { int execute(int a, int b); }
+
+public class FunctionParameter {
+
+    public static int performOperation(int a, int b, Operation operation) { return operation.execute(a, b); }
+
+    public static int passFunctionUsingAnnonymousClass(int a, int b) {
+        return performOperation(a, b, new Operation() {
+            @Override
+            public int execute(int a, int b) {
+                return a + b;
+            }
+        });
+    }
+
+    public static int passFunctionUsingLambda(int a, int b) {
+        return performOperation(a, b, (i, k) -> i + k);
+    }
+
+    private static int add(int a, int b) { return a + b; }
+
+    public static int passFunctionUsingMethodReferrences(int a, int b) {
+        return performOperation(a, b, FunctionParameter::add);
+    }
+
+    private static int executeFunction(BiFunction<Integer, Integer, Integer> function, int a, int b) { return function.apply(a, b);  }
+
+    public static int passFunctionUsingFunction(int a, int b) {
+        return executeFunction((i, k) -> i + k, a, b);
+    }
+
+    private static int executeCallable(Callable<Integer> task) throws Exception {
+        return task.call();
+    }
+
+    public static int passFunctionUsingCallable(int a, int b) throws Exception {
+        Callable<Integer> task = () -> a + b;
+        return executeCallable(task);
+    }
+}

core-java-modules/core-java-function/src/test/java/com/baeldung/functionparameter/FunctionParameterUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.functionparameter;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class FunctionParameterUnitTest {
+
+    @Test
+    void givenAddFunction_whenUsingAnnonymousClass_thenReturnSumValue() {
+        assertEquals(8, FunctionParameter.passFunctionUsingAnnonymousClass(5, 3));
+        assertEquals(0, FunctionParameter.passFunctionUsingAnnonymousClass(100, -100));
+    }
+
+    @Test
+    void givenAddFunction_whenUsingLambda_thenReturnSumValue() {
+        assertEquals(8, FunctionParameter.passFunctionUsingLambda(5, 3));
+        assertEquals(0, FunctionParameter.passFunctionUsingLambda(100, -100));
+    }
+
+    @Test
+    void givenAddFunction_whenUsingMethodReferrences_thenReturnSumValue() {
+        assertEquals(8, FunctionParameter.passFunctionUsingMethodReferrences(5, 3));
+        assertEquals(0, FunctionParameter.passFunctionUsingMethodReferrences(100, -100));
+    }
+
+    @Test
+    void givenAddFunction_whenUsingFunction_thenReturnSumValue() {
+        assertEquals(8, FunctionParameter.passFunctionUsingFunction(5, 3));
+        assertEquals(0, FunctionParameter.passFunctionUsingFunction(100, -100));
+    }
+
+    @Test
+    void givenAddFunction_whenUsingCallable_thenReturnSumValue() throws Exception {
+        assertEquals(8, FunctionParameter.passFunctionUsingCallable(5, 3));
+        assertEquals(0, FunctionParameter.passFunctionUsingCallable(100, -100));
+    }
+}