Eagerly initialize ZERO_NANOS constant

spring-context/src/main/java/org/springframework/scheduling/support/BitsCronField.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -33,13 +33,10 @@ import org.springframework.util.StringUtils;
  */
 final class BitsCronField extends CronField {
 
+	public static BitsCronField ZERO_NANOS = forZeroNanos();
+
 	private static final long MASK = 0xFFFFFFFFFFFFFFFFL;
 
-
-	@Nullable
-	private static BitsCronField zeroNanos = null;
-
-
 	// we store at most 60 bits, for seconds and minutes, so a 64-bit long suffices
 	private long bits;
 
@@ -48,16 +45,14 @@ final class BitsCronField extends CronField {
 		super(type);
 	}
 
+
 	/**
 	 * Return a {@code BitsCronField} enabled for 0 nanoseconds.
 	 */
-	public static BitsCronField zeroNanos() {
-		if (zeroNanos == null) {
-			BitsCronField field = new BitsCronField(Type.NANO);
-			field.setBit(0);
-			zeroNanos = field;
-		}
-		return zeroNanos;
+	private static BitsCronField forZeroNanos() {
+		BitsCronField field = new BitsCronField(Type.NANO);
+		field.setBit(0);
+		return field;
 	}
 
 	/**
@@ -108,7 +103,6 @@ final class BitsCronField extends CronField {
 		return result;
 	}
 
-
 	private static BitsCronField parseDate(String value, BitsCronField.Type type) {
 		if (value.equals("?")) {
 			value = "*";
@@ -174,6 +168,7 @@ final class BitsCronField extends CronField {
 		}
 	}
 
+
 	@Nullable
 	@Override
 	public <T extends Temporal & Comparable<? super T>> T nextOrSame(T temporal) {
@@ -217,7 +212,6 @@ final class BitsCronField extends CronField {
 		else {
 			return -1;
 		}
-
 	}
 
 	private void setBits(ValueRange range) {
@@ -250,20 +244,16 @@ final class BitsCronField extends CronField {
 		this.bits &= ~(1L << index);
 	}
 
+
 	@Override
-	public int hashCode() {
-		return Long.hashCode(this.bits);
+	public boolean equals(Object other) {
+		return (this == other || (other instanceof BitsCronField that &&
+				type() == that.type() && this.bits == that.bits));
 	}
 
 	@Override
-	public boolean equals(@Nullable Object o) {
-		if (this == o) {
-			return true;
-		}
-		if (!(o instanceof BitsCronField other)) {
-			return false;
-		}
-		return type() == other.type() && this.bits == other.bits;
+	public int hashCode() {
+		return Long.hashCode(this.bits);
 	}
 
 	@Override

spring-context/src/main/java/org/springframework/scheduling/support/CronField.java

@@ -29,7 +29,7 @@ import org.springframework.util.StringUtils;
 
 /**
  * Single field in a cron pattern. Created using the {@code parse*} methods,
- * main and only entry point is {@link #nextOrSame(Temporal)}.
+ * the main and only entry point is {@link #nextOrSame(Temporal)}.
  *
  * <p>Supports a Quartz day-of-month/week field with an L/# expression. Follows
  * common cron conventions in every other respect, including 0-6 for SUN-SAT
@@ -60,7 +60,7 @@ abstract class CronField {
 	 * Return a {@code CronField} enabled for 0 nanoseconds.
 	 */
 	public static CronField zeroNanos() {
-		return BitsCronField.zeroNanos();
+		return BitsCronField.ZERO_NANOS;
 	}
 
 	/**
@@ -186,7 +186,6 @@ abstract class CronField {
 		MONTH(ChronoField.MONTH_OF_YEAR, ChronoUnit.YEARS, ChronoField.DAY_OF_MONTH, ChronoField.HOUR_OF_DAY, ChronoField.MINUTE_OF_HOUR, ChronoField.SECOND_OF_MINUTE, ChronoField.NANO_OF_SECOND),
 		DAY_OF_WEEK(ChronoField.DAY_OF_WEEK, ChronoUnit.WEEKS, ChronoField.HOUR_OF_DAY, ChronoField.MINUTE_OF_HOUR, ChronoField.SECOND_OF_MINUTE, ChronoField.NANO_OF_SECOND);
 
-
 		private final ChronoField field;
 
 		private final ChronoUnit higherOrder;

spring-context/src/main/java/org/springframework/scheduling/support/QuartzCronField.java

@@ -336,6 +336,7 @@ final class QuartzCronField extends CronField {
 		}
 	}
 
+
 	@Override
 	public <T extends Temporal & Comparable<? super T>> T nextOrSame(T temporal) {
 		T result = adjust(temporal);
@@ -352,7 +353,6 @@ final class QuartzCronField extends CronField {
 		return result;
 	}
 
-
 	@Nullable
 	@SuppressWarnings("unchecked")
 	private <T extends Temporal & Comparable<? super T>> T adjust(T temporal) {