adding built-in java annotation examples (#3087)

core-java-8/src/main/java/com/baeldung/annotations/ClassWithAnnotation.java

@@ -0,0 +1,5 @@
+package com.baeldung.annotations;
+
+@Deprecated
+class ClassWithAnnotation {
+}

core-java-8/src/main/java/com/baeldung/annotations/ClassWithDeprecatedMethod.java

@@ -0,0 +1,9 @@
+package com.baeldung.annotations;
+
+class ClassWithDeprecatedMethod {
+
+    @Deprecated
+    static void deprecatedMethod() {
+
+    }
+}

core-java-8/src/main/java/com/baeldung/annotations/ClassWithSafeVarargs.java

@@ -0,0 +1,11 @@
+package com.baeldung.annotations;
+
+class ClassWithSafeVarargs<T> {
+
+    @SafeVarargs
+    final void iterateOverVarargs(T... args) {
+        for (T x : args) {
+            // do stuff with x
+        }
+    }
+}

core-java-8/src/main/java/com/baeldung/annotations/ClassWithSuppressWarnings.java

@@ -0,0 +1,9 @@
+package com.baeldung.annotations;
+
+class ClassWithSuppressWarnings {
+
+    @SuppressWarnings("deprecation")
+    void useDeprecatedMethod() {
+        ClassWithDeprecatedMethod.deprecatedMethod(); // no warning is generated here
+    }
+}

core-java-8/src/main/java/com/baeldung/annotations/IntConsumer.java

@@ -0,0 +1,8 @@
+package com.baeldung.annotations;
+
+@FunctionalInterface
+interface IntConsumer {
+
+    void accept(Integer number);
+
+}

core-java-8/src/main/java/com/baeldung/annotations/Interval.java

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+package com.baeldung.annotations;
+
+import java.lang.annotation.Repeatable;
+
+@Repeatable(Intervals.class)
+@interface Interval {
+    int hour() default 1;
+}

core-java-8/src/main/java/com/baeldung/annotations/IntervalUsage.java

@@ -0,0 +1,9 @@
+package com.baeldung.annotations;
+
+public class IntervalUsage {
+
+    @Interval(hour = 17)
+    @Interval(hour = 13)
+    void doPeriodicCleanup() {
+    }
+}

core-java-8/src/main/java/com/baeldung/annotations/Intervals.java

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+package com.baeldung.annotations;
+
+@interface Intervals {
+    Interval[] value();
+}

core-java-8/src/main/java/com/baeldung/annotations/MyAnnotation.java

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+package com.baeldung.annotations;
+
+import java.lang.annotation.*;
+
+@Inherited
+@Documented
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.LOCAL_VARIABLE, ElementType.FIELD})
+@interface MyAnnotation {
+
+}

core-java-8/src/main/java/com/baeldung/annotations/MyAnnotationTarget.java

@@ -0,0 +1,16 @@
+package com.baeldung.annotations;
+
+class MyAnnotationTarget {
+
+    // this is OK
+    @MyAnnotation
+    String someField;
+
+    // @MyAnnotation <- this is invalid usage!
+    void doSomething() {
+
+        // this also works
+        @MyAnnotation
+        String localVariable;
+    }
+}

core-java-8/src/main/java/com/baeldung/annotations/MyOperation.java

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+package com.baeldung.annotations;
+
+interface MyOperation {
+
+    void perform();
+}

core-java-8/src/main/java/com/baeldung/annotations/MyOperationImpl.java

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+package com.baeldung.annotations;
+
+class MyOperationImpl implements MyOperation {
+
+    @Override
+    public void perform() {
+
+    }
+}