BAEL-6206 code for the JetBrains @Contract annotation article

2023-03-09 23:08:06 +01:00
parent 9a26f2c212
commit 6d2745231c
5 changed files with 171 additions and 2 deletions
@@ -0,0 +1,112 @@
+package com.baeldung.annotations;
+
+import java.util.List;
+
+import org.apache.commons.lang3.StringUtils;
+import org.jetbrains.annotations.Contract;
+
+public class Demo {
+
+    @Contract("_ -> new")
+    Person fromName(String name) {
+        return new Person().withName(name);
+    }
+
+    @Contract(" -> fail")
+    void alwaysFail() {
+        throw new RuntimeException();
+    }
+
+    @Contract(" -> fail")
+    void doNothingWithWrongContract() {
+
+    }
+
+    @Contract("_, null -> null; null, _ -> param2; _, !null -> !null")
+    String concatenateOnlyIfSecondArgumentIsNotNull(String head, String tail) {
+        if (tail == null) {
+            return null;
+        }
+        if (head == null) {
+            return tail;
+        }
+        return head + tail;
+    }
+
+    void uselessNullCheck() {
+        String head = "1234";
+        String tail = "5678";
+        String concatenation = concatenateOnlyIfSecondArgumentIsNotNull(head, tail);
+        if (concatenation != null) {
+            System.out.println(concatenation);
+        }
+    }
+
+    void uselessNullCheckOnInferredAnnotation() {
+        if (StringUtils.isEmpty(null)) {
+            System.out.println("baeldung");
+        }
+    }
+
+    @Contract(pure = true)
+    String replace(String string, char oldChar, char newChar) {
+        return string.replace(oldChar, newChar);
+    }
+
+    @Contract(value = "true -> false; false -> true", pure = true)
+    boolean not(boolean input) {
+        return !input;
+    }
+
+    @Contract("true -> new")
+    void contractExpectsWrongParameterType(List<Integer> integers) {
+
+    }
+
+    @Contract("_, _ -> new")
+    void contractExpectsMoreParametersThanMethodHas(String s) {
+
+    }
+
+    @Contract("_ -> _; null -> !null")
+    String secondContractClauseNotReachable(String s) {
+        return "";
+    }
+
+    @Contract("_ -> true")
+    void contractExpectsWrongReturnType(String s) {
+
+    }
+
+    // NB: the following examples demonstrate how to use the mutates attribute of the annotation
+    // This attribute is currently experimental and could be changed or removed in the future
+    @Contract(mutates = "param")
+    void incrementArrayFirstElement(Integer[] integers) {
+        if (integers.length > 0) {
+            integers[0] = integers[0] + 1;
+        }
+    }
+
+    @Contract(pure = true, mutates = "param")
+    void impossibleToMutateParamInPureFunction(List<String> strings) {
+        if (strings != null) {
+            strings.forEach(System.out::println);
+        }
+    }
+
+    @Contract(mutates = "param3")
+    void impossibleToMutateThirdParamWhenMethodHasOnlyTwoParams(int a, int b) {
+
+    }
+
+    @Contract(mutates = "param")
+    void impossibleToMutableImmutableType(String s) {
+
+    }
+
+    @Contract(mutates = "this")
+    static void impossibleToMutateThisInStaticMethod() {
+
+    }
+
+}
@@ -0,0 +1,15 @@
+package com.baeldung.annotations;
+
+import org.jetbrains.annotations.Contract;
+
+public class Person {
+
+    String name;
+
+    @Contract("_ -> this")
+    Person withName(String name) {
+        this.name = name;
+        return this;
+    }
+
+}