Code for "Lambda Expressions and Functional Interfaces. Best Practices and Tips" article

core-java-8/src/main/java/org/baeldung/Adder.java

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+package org.baeldung;
+
+import java.util.function.Consumer;
+import java.util.function.Function;
+
+public interface Adder {
+
+    String addWithFunction(Function<String, String> f);
+
+    void addWithConsumer(Consumer<Integer> f);
+
+}

core-java-8/src/main/java/org/baeldung/AdderImpl.java

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+package org.baeldung;
+
+import java.util.function.Consumer;
+import java.util.function.Function;
+
+public class AdderImpl implements Adder {
+
+    @Override
+    public  String addWithFunction(Function<String, String> f) {
+        return f.apply("Something ");
+    }
+
+    @Override
+    public void addWithConsumer(Consumer<Integer> f) {}
+
+}

core-java-8/src/main/java/org/baeldung/Bar.java

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+package org.baeldung;
+
+@FunctionalInterface
+public interface Bar {
+
+    String method(String string);
+
+    default String defaultMethod() {
+        return "String from Bar";
+    }
+
+}

core-java-8/src/main/java/org/baeldung/Baz.java

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+package org.baeldung;
+
+@FunctionalInterface
+public interface Baz {
+
+    String method(String string);
+
+    default String defaultMethod() {
+        return "String from Baz";
+    }
+}

core-java-8/src/main/java/org/baeldung/Foo.java

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+package org.baeldung;
+
+@FunctionalInterface
+public interface Foo {
+
+    String method(String string);
+
+    default void defaultMethod() {}
+}

core-java-8/src/main/java/org/baeldung/FooExtended.java

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+package org.baeldung;
+
+@FunctionalInterface
+public interface FooExtended extends Baz, Bar {
+
+    @Override
+    default String defaultMethod() {
+        return Bar.super.defaultMethod();
+    }
+
+}

core-java-8/src/main/java/org/baeldung/UseFoo.java

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+package org.baeldung;
+
+import java.util.function.Function;
+
+public class UseFoo {
+
+    private String value = "Enclosing scope value";
+
+    public String add(String string, Foo foo) {
+        return foo.method(string);
+    }
+
+    public String addWithStandardFI(String string, Function<String, String> fn) {
+        return fn.apply(string);
+    }
+
+    public String scopeExperiment() {
+        Foo fooIC = new Foo() {
+            String value = "Inner class value";
+
+            @Override
+            public String method(String string) {
+                return this.value;
+            }
+        };
+        String resultIC = fooIC.method("");
+
+        Foo fooLambda = parameter -> {
+            String value = "Lambda value";
+            return this.value;
+        };
+        String resultLambda = fooLambda.method("");
+
+        return "Results: resultIC = " + resultIC +
+                ", resultLambda = " + resultLambda;
+    }
+
+    
+}