BAEL2489 - Avoid check for null statement in Java (#6411)

* BAEL2489 - Avoid check for null statement in Java

* BAEL2489 Avoid check for null statement in Java

* BAEL2489 Avoid check for null statement in Java

* BAEL2489 Avoid check for null statement in Java

* BAEL2489 Avoid check for null statement in Java

* BAEL2489 Avoid check for null statement in Java - Removing unused pom changes

* BAEL2489 Avoid check for null statement in Java - Removing unused pom changes

* Delete pom.xml

Removing unused changes in core-java

* BAEL2489 Avoid check for null statement in Java - Removing unused pom changes

patterns/design-patterns-2/pom.xml

@@ -15,11 +15,29 @@
     </parent>
 
     <dependencies>
+        <dependency>
+            <groupId>org.jetbrains</groupId>
+            <artifactId>annotations</artifactId>
+            <version>${intellij.annotations.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
     </dependencies>
     
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>
+        <intellij.annotations.version>16.0.2</intellij.annotations.version>
+        <commons-lang3.version>3.5</commons-lang3.version>
     </properties>
 </project>

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/APIContracts.java

@@ -0,0 +1,30 @@
+package com.baeldung.nulls;
+
+public class APIContracts {
+
+    /**
+     * Prints the value of {@code param} if not null. Prints {@code null} otherwise.
+     *
+     * @param param
+     */
+    public void print(Object param) {
+        System.out.println("Printing " + param);
+    }
+
+    /**
+     * @return non null result
+     * @throws Exception - if result is null
+     */
+    public Object process() throws Exception {
+        Object result = doSomething();
+        if (result == null) {
+            throw new Exception("Processing fail. Got a null response");
+        } else {
+            return result;
+        }
+    }
+
+    private Object doSomething() {
+        return null;
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/Assertions.java

@@ -0,0 +1,13 @@
+package com.baeldung.nulls;
+
+public class Assertions {
+    
+    public void accept(Object param){
+        assert param != null;
+        
+        doSomething(param);
+    }
+
+    private void doSomething(Object param) {
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/EmptyCollections.java

@@ -0,0 +1,25 @@
+package com.baeldung.nulls;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class EmptyCollections {
+
+    public List<String> names() {
+        if (userExist()) {
+            return Stream.of(readName()).collect(Collectors.toList());
+        } else {
+            return Collections.emptyList();
+        }
+    }
+
+    private boolean userExist() {
+        return false;
+    }
+
+    private String readName() {
+        return "test";
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/FindBugsAnnotations.java

@@ -0,0 +1,30 @@
+package com.baeldung.nulls;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+
+public class FindBugsAnnotations {
+
+    public void accept(@NotNull Object param) {
+        System.out.println(param.toString());
+    }
+
+    public void print(@Nullable Object param) {
+        System.out.println("Printing " + param);
+    }
+
+    @NotNull
+    public Object process() throws Exception {
+        Object result = doSomething();
+        if (result == null) {
+            throw new Exception("Processing fail. Got a null response");
+        } else {
+            return result;
+        }
+    }
+
+    private Object doSomething() {
+        return null;
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/Preconditions.java

@@ -0,0 +1,39 @@
+package com.baeldung.nulls;
+
+public class Preconditions {
+
+    public void goodAccept(String one, String two, String three) {
+        if (one == null || two == null || three == null) {
+            throw new IllegalArgumentException();
+        }
+
+        process(one);
+        process(two);
+        process(three);
+    }
+
+    public void badAccept(String one, String two, String three) {
+        if (one == null) {
+            throw new IllegalArgumentException();
+        } else {
+            process(one);
+        }
+
+        if (two == null) {
+            throw new IllegalArgumentException();
+        } else {
+            process(two);
+        }
+
+        if (three == null) {
+            throw new IllegalArgumentException();
+        } else {
+            process(three);
+        }
+
+    }
+
+    private void process(String one) {
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/PrimitivesAndWrapper.java

@@ -0,0 +1,21 @@
+package com.baeldung.nulls;
+
+public class PrimitivesAndWrapper {
+
+    public static int primitiveSum(int a, int b) {
+        return a + b;
+    }
+
+    public static Integer wrapperSum(Integer a, Integer b) {
+        return a + b;
+    }
+
+    public static Integer goodSum(Integer a, Integer b) {
+        if (a != null && b != null) {
+            return a + b;
+        } else {
+            throw new IllegalArgumentException();
+        }
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/UsingLombok.java

@@ -0,0 +1,10 @@
+package com.baeldung.nulls;
+
+import lombok.NonNull;
+
+public class UsingLombok {
+
+    public void accept(@NonNull Object param){
+        System.out.println(param);
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/UsingObjects.java

@@ -0,0 +1,11 @@
+package com.baeldung.nulls;
+
+import java.util.Objects;
+
+public class UsingObjects {
+
+    public void accept(Object param) {
+        Objects.requireNonNull(param);
+        // doSomething()
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/UsingOptional.java

@@ -0,0 +1,27 @@
+package com.baeldung.nulls;
+
+import java.util.Optional;
+
+public class UsingOptional {
+
+    public Optional<Object> process(boolean processed) {
+
+        String response = doSomething(processed);
+
+        if (response == null) {
+            return Optional.empty();
+        }
+
+        return Optional.of(response);
+    }
+
+    private String doSomething(boolean processed) {
+
+        if (processed) {
+            return "passed";
+        } else {
+            return null;
+        }
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/UsingStringUtils.java

@@ -0,0 +1,22 @@
+package com.baeldung.nulls;
+
+import org.apache.commons.lang3.StringUtils;
+
+public class UsingStringUtils {
+
+    public void accept(String param) {
+        if (StringUtils.isNotEmpty(param)) {
+            System.out.println(param);
+        } else {
+            throw new IllegalArgumentException();
+        }
+    }
+
+    public void acceptOnlyNonBlank(String param) {
+        if (StringUtils.isNotBlank(param)) {
+            System.out.println(param);
+        } else {
+            throw new IllegalArgumentException();
+        }
+    }
+}

patterns/design-patterns-2/src/test/java/com/baeldung/nulls/PrimitivesAndWrapperUnitTest.java

@@ -0,0 +1,35 @@
+package com.baeldung.nulls;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class PrimitivesAndWrapperUnitTest {
+
+    @Test
+    public void givenBothArgsNonNull_whenCallingWrapperSum_thenReturnSum() {
+
+        Integer sum = PrimitivesAndWrapper.wrapperSum(0, 0);
+
+        assertEquals(0, sum.intValue());
+    }
+
+    @Test()
+    public void givenOneArgIsNull_whenCallingWrapperSum_thenThrowNullPointerException() {
+        assertThrows(NullPointerException.class, () -> PrimitivesAndWrapper.wrapperSum(null, 2));
+    }
+
+    @Test()
+    public void givenBothArgsNull_whenCallingWrapperSum_thenThrowNullPointerException() {
+        assertThrows(NullPointerException.class, () -> PrimitivesAndWrapper.wrapperSum(null, null));
+    }
+
+    @Test()
+    public void givenOneArgNull_whenCallingGoodSum_thenThrowIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> PrimitivesAndWrapper.goodSum(null, 2));
+    }
+
+
+
+}

patterns/design-patterns-2/src/test/java/com/baeldung/nulls/UsingLombokUnitTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.nulls;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class UsingLombokUnitTest {
+
+    private UsingLombok classUnderTest;
+
+    @BeforeEach
+    public void setup() {
+        classUnderTest = new UsingLombok();
+    }
+
+    @Test
+    public void whenNullArg_thenThrowNullPointerException() {
+
+        assertThrows(NullPointerException.class, () -> classUnderTest.accept(null));
+
+    }
+
+}

patterns/design-patterns-2/src/test/java/com/baeldung/nulls/UsingObjectsUnitTest.java

@@ -0,0 +1,30 @@
+package com.baeldung.nulls;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class UsingObjectsUnitTest {
+
+    private UsingObjects classUnderTest;
+
+    @BeforeEach
+    public void setup() {
+        classUnderTest = new UsingObjects();
+    }
+
+    @Test
+    public void whenArgIsNull_thenThrowException() {
+
+        assertThrows(NullPointerException.class, () -> classUnderTest.accept(null));
+    }
+
+    @Test
+    public void whenArgIsNonNull_thenDoesNotThrowException() {
+
+        assertDoesNotThrow(() -> classUnderTest.accept("test    "));
+    }
+
+}

patterns/design-patterns-2/src/test/java/com/baeldung/nulls/UsingOptionalUnitTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.nulls;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class UsingOptionalUnitTest {
+
+    private UsingOptional classUnderTest;
+
+    @BeforeEach
+    public void setup() {
+        classUnderTest = new UsingOptional();
+    }
+
+    @Test
+    public void whenArgIsFalse_thenReturnEmptyResponse() {
+
+        Optional<Object> result = classUnderTest.process(false);
+
+        assertFalse(result.isPresent());
+    }
+
+    @Test
+    public void whenArgIsTrue_thenReturnValidResponse() {
+
+        Optional<Object> result = classUnderTest.process(true);
+
+        assertTrue(result.isPresent());
+    }
+
+    @Test
+    public void whenArgIsFalse_thenChainResponseAndThrowException() {
+
+        assertThrows(Exception.class, () -> classUnderTest.process(false).orElseThrow(() -> new Exception()));
+    }
+}

patterns/design-patterns-2/src/test/java/com/baeldung/nulls/UsingStringUtilsUnitTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.nulls;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class UsingStringUtilsUnitTest {
+
+    private UsingStringUtils classUnderTest;
+
+    @BeforeEach
+    public void setup() {
+        classUnderTest = new UsingStringUtils();
+    }
+
+    @Test
+    public void givenArgIsNull_whenCallingAccept_throwIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> classUnderTest.accept(null));
+    }
+
+    @Test
+    public void givenArgIsEmpty_whenCallingAccept_throwIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> classUnderTest.accept(""));
+    }
+
+    @Test
+    public void givenArgIsNull_whenCallingAcceptOnlyNonBlank_throwIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> classUnderTest.acceptOnlyNonBlank(null));
+    }
+
+    @Test
+    public void givenArgIsEmpty_whenCallingAcceptOnlyNonBlank_throwIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> classUnderTest.acceptOnlyNonBlank(""));
+    }
+
+    @Test
+    public void givenArgIsBlank_whenCallingAcceptOnlyNonBlank_throwIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> classUnderTest.acceptOnlyNonBlank(" "));
+    }
+
+}