Проверка на null

if(somemethod!=null){
}

import java.util.NoSuchElementException;
import java.util.Objects;
 
/**
 * @author mutagen
 */
public class OptionalDemo {
 
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        CustomClass customClass = new CustomClass();
        Optional<String> rezNotNull = customClass.myNotNullMethod(100);
        Optional<String> rezCouldBeNull = customClass.myCouldBeNullMethod(100);
        if (rezNotNull.isPresent()) {
            System.out.println("we have value so we can proceed: " + rezNotNull.get());
        }
 
        if (rezCouldBeNull.isPresent()) {
            // we never get null as response
        } else {
            System.out.println("do nothing and we never get null as response");
        }
    }
 
    static class CustomClass {
 
        public Optional<String> myNotNullMethod(int i) {
            // do smth
            return new Optional<>(String.valueOf(i));
        }
 
        public Optional<String> myCouldBeNullMethod(int i) {
            // do smth
            return new Optional<>();
        }
    }
 
    static final class Optional<T> {
 
        /**
         * Common instance for {@code empty()}.
         */
        private static final Optional<?> EMPTY = new Optional<>();
        /**
         * If non-null, the value; if null, indicates no value is present
         */
        private final T value;
 
        /**
         * Construct an empty instance.
         *
         * @implNote Generally only one empty instance, {@link Optional#EMPTY}, should exist per VM.
         */
        private Optional() {
            this.value = null;
        }
 
        /**
         * Returns an empty {@code Optional} instance. No value is present for this Optional.
         *
         * @apiNote Though it may be tempting to do so, avoid testing if an object is empty by comparing with {@code ==}
         * against instances returned by {@code Option.empty()}. There is no guarantee that it is a singleton. Instead,
         * use {@link #isPresent()}.
         *
         * @param <T> Type of the non-existent value
         * @return an empty {@code Optional}
         */
        public static <T> Optional<T> empty() {
            @SuppressWarnings("unchecked")
            Optional<T> t = (Optional<T>) EMPTY;
            return t;
        }
 
        /**
         * Construct an instance with the value present.
         *
         * @param value the non-null value to be present
         */
        private Optional(T value) {
            this.value = Objects.requireNonNull(value);
        }
 
        /**
         * Return an {@code Optional} with the specified present value.
         *
         * @param value the value to be present, which must be non-null
         * @return an {@code Optional} with the value present
         */
        public static <T> Optional<T> of(T value) {
            return new Optional<>(value);
        }
 
        /**
         * If a value is present in this {@code Optional}, returns the value, otherwise throws
         * {@code NoSuchElementException}.
         *
         * @return the non-null value held by this {@code Optional}
         * @throws NoSuchElementException if there is no value present
         *
         * @see Optional#isPresent()
         */
        public T get() {
            if (value == null) {
                throw new NoSuchElementException("No value present");
            }
            return value;
        }
 
        /**
         * Return {@code true} if there is a value present, otherwise {@code false}.
         *
         * @return {@code true} if there is a value present, otherwise {@code false}
         */
        public boolean isPresent() {
            return value != null;
        }
 
        /**
         * Have the specified consumer accept the value if a value is present, otherwise do nothing.
         *
         * @param consumer block to be executed if a value is present
         * @throws NullPointerException if value is present and {@code consumer} is null
         */
//        public void ifPresent(Consumer<? super T> consumer) {
//            if (value != null) {
//                consumer.accept(value);
//            }
//        }
        /**
         * Return the value if present, otherwise return {@code other}.
         *
         * @param other the value to be returned if there is no value present, may be null
         * @return the value, if present, otherwise {@code other}
         */
        public T orElse(T other) {
            return value != null ? value : other;
        }
 
        /**
         * Return the value if present, otherwise invoke {@code other} and return the result of that invocation.
         *
         * @param other a {@code Supplier} whose result is returned if no value is present
         * @return the value if present otherwise the result of {@code other.get()}
         * @throws NullPointerException if value is not present and {@code other} is null
         */
//        public T orElseGet(Supplier<? extends T> other) {
//            return value != null ? value : other.get();
//        }
        /**
         * Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.
         *
         * @apiNote A method reference to the exception constructor with an empty argument list can be used as the
         * supplier. For example, {@code IllegalStateException::new}
         *
         * @param <X> Type of the exception to be thrown
         * @param exceptionSupplier The supplier which will return the exception to be thrown
         * @return the present value
         * @throws X if there is no value present
         * @throws NullPointerException if no value is present and {@code exceptionSupplier} is null
         */
//        public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
//            if (value != null) {
//                return value;
//            } else {
//                throw exceptionSupplier.get();
//            }
//        }
        /**
         * Indicates whether some other object is "equal to" this Optional. The other object is considered equal if:
         * <ul>
         * <li>it is also an {@code Optional} and;
         * <li>both instances have no value present or;
         * <li>the present values are "equal to" each other via {@code equals()}.
         * </ul>
         *
         * @param obj an object to be tested for equality
         * @return {code true} if the other object is "equal to" this object otherwise {@code false}
         */
        @Override
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }
 
            if (!(obj instanceof Optional)) {
                return false;
            }
 
            Optional other = (Optional) obj;
            return Objects.equals(value, other.value);
        }
 
        /**
         * Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.
         *
         * @return hash code value of the present value or 0 if no value is present
         */
        @Override
        public int hashCode() {
            return Objects.hashCode(value);
        }
 
        /**
         * Returns a non-empty string representation of this Optional suitable for debugging. The exact presentation
         * format is unspecified and may vary between implementations and versions.
         *
         * @implSpec If a value is present the result must include its string representation in the result. Empty and
         * present Optionals must be unambiguously differentiable.
         *
         * @return the string representation of this instance
         */
        @Override
        public String toString() {
            return value != null
                    ? String.format("Optional[%s]", value)
                    : "Optional.empty";
        }
    }
}

Object sync = null;
 
//...
 
try{
    synchronized(sync){
        sync.wait();
    }
} catch(NullPointerException ex){
    sync = new Object();
    synchronized(sync){
        sync.wait();
    }
}

 public Optional<String> myNotNullMethod(Integer i) {
            // do smth
            return new Optional<>(String.valueOf(i));
        }

 Optional<String> rezNotNull = customClass.myNotNullMethod(null);

    public Integer checkSMTHG(Integer value) {
        if (value == null) {
            return null;
        }
 
        int CONST = 50;
 
        if (value > CONST) {
            return 1;
        }
        if (value < CONST) {
            return -1;
        }
        return 0;
    }