BAEL2489 - Avoid check for null statement in Java

core-java/src/main/java/com/baeldung/nulls/APIContracts.java

@@ -0,0 +1,29 @@
+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;
+    }
+}

core-java/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) {
+    }
+}

core-java/src/main/java/com/baeldung/nulls/EmptyCollections.java

@@ -0,0 +1,24 @@
+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";
+    }
+}

core-java/src/main/java/com/baeldung/nulls/FindBugsAnnotations.java

@@ -0,0 +1,28 @@
+package com.baeldung.nulls;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+public class FindBugsAnnotations {
+
+    public void accept(@Nonnull Object param) {
+        System.out.println(param.toString());
+    }
+
+    public void print(@Nullable Object param) {
+        System.out.println("Printing " + param);
+    }
+
+    @Nonnull
+    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;
+    }
+}

core-java/src/main/java/com/baeldung/nulls/Preconditions.java

@@ -0,0 +1,32 @@
+package com.baeldung.nulls;
+
+public class Preconditions {
+
+    public void goodAccept(String one, String two, String three) {
+        if (null == one || null == two || three == null)
+            throw new IllegalArgumentException();
+    }
+
+    public void badAccept(String one, String two, String three){
+        if (null == one)
+            throw new IllegalArgumentException();
+        else
+            process(one);
+
+        if (null == two)
+            throw new IllegalArgumentException();
+        else
+            process(two);
+
+        if (null == three)
+            throw new IllegalArgumentException();
+        else
+            process(three);
+
+    }
+
+    private void process(String one) {
+    }
+
+
+}

core-java/src/main/java/com/baeldung/nulls/PrimitivesAndWrapper.java

@@ -0,0 +1,24 @@
+package com.baeldung.nulls;
+
+public class PrimitivesAndWrapper {
+
+    public static int sum(int a, int b) {
+        return a + b;
+    }
+
+    public static Integer sum(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();
+    }
+
+    public static void main(String[] args) {
+        sum(0, 0);
+        sum(null, null);
+    }
+}

core-java/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);
+    }
+}

core-java/src/main/java/com/baeldung/nulls/UsingObjects.java

@@ -0,0 +1,24 @@
+package com.baeldung.nulls;
+
+import java.util.Objects;
+
+public class UsingObjects {
+
+    private String checked;
+
+    public void accept(Object param) {
+        try {
+            Objects.requireNonNull(param);
+        } catch (NullPointerException e) {
+            //doSomethingElseToo
+            e.printStackTrace();
+        }
+    }
+
+    public void caller() throws Exception {
+        if (Objects.nonNull(checked))
+            accept(checked);
+        else
+            throw new Exception();
+    }
+}

core-java/src/main/java/com/baeldung/nulls/UsingOptional.java

@@ -0,0 +1,23 @@
+package com.baeldung.nulls;
+
+import java.util.Optional;
+
+public class UsingOptional {
+
+    public Optional<Object> process() {
+        if (isProcessed())
+            return Optional.of("dummy");
+        else
+            return Optional.empty();
+    }
+
+    public void caller() {
+        Optional<Object> result = process();
+        result.ifPresent(p -> System.out.println(p));
+        result.orElseThrow(() -> new IllegalArgumentException());
+    }
+
+    private boolean isProcessed() {
+        return false;
+    }
+}

core-java/src/main/java/com/baeldung/nulls/UsingStringUtils.java

@@ -0,0 +1,17 @@
+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);
+    }
+
+    public void acceptOnlyNonBlank(String param) {
+        if (StringUtils.isNotBlank(param))
+            System.out.println(param);
+    }
+}