[6to7] Restore public DDTraceId class API

dd-trace-api/src/main/java/datadog/trace/api/DD128bTraceId.java

@@ -14,7 +14,7 @@
  * #highOrderBits} is set to <code>0</code> and {@link #lowOrderBits} contains a unique and random
  * 63-bit id.
  */
-public class DD128bTraceId implements DDTraceId {
+public class DD128bTraceId extends DDTraceId {
   public static final DD128bTraceId ZERO =
       new DD128bTraceId(0, 0, "00000000000000000000000000000000");
   /** Represents the high-order 64 bits of the 128-bit trace id. */

dd-trace-api/src/main/java/datadog/trace/api/DD64bTraceId.java

@@ -9,9 +9,7 @@
  * representations. The decimal string representation is either kept from parsing, or generated on
  * demand and cached.
  */
-public class DD64bTraceId implements DDTraceId {
-
-  public static final DD64bTraceId ZERO = new DD64bTraceId(0, "0");
+public class DD64bTraceId extends DDTraceId {
   public static final DD64bTraceId MAX =
       new DD64bTraceId(-1, "18446744073709551615"); // All bits set
 
@@ -61,9 +59,15 @@ public static DD64bTraceId fromHex(String s) throws NumberFormatException {
   }
 
   static DD64bTraceId create(long id, String str) {
-    if (id == 0) return ZERO;
-    if (id == -1) return MAX;
-    return new DD64bTraceId(id, str);
+    // ZERO constant is created and stored by the parent class as part of its API contract
+    // But initialized by this 64-bit child class. Ensures uniqueness of ZERO once created.
+    if (id == 0 && ZERO != null) {
+      return (DD64bTraceId) ZERO;
+    } else if (id == -1) {
+      return MAX;
+    } else {
+      return new DD64bTraceId(id, str);
+    }
   }
 
   @Override

dd-trace-api/src/main/java/datadog/trace/api/DDTraceId.java

@@ -8,11 +8,11 @@
  * <p>It contains parsing and formatting to string for both decimal and hexadecimal representations.
  * The string representations are either kept from parsing, or generated on demand and cached.
  */
-public interface DDTraceId {
+public abstract class DDTraceId {
   /** Invalid TraceId value used to denote no TraceId. */
-  DDTraceId ZERO = from(0);
+  public static final DDTraceId ZERO = from(0);
   /** Convenience constant used from tests */
-  DDTraceId ONE = from(1);
+  public static final DDTraceId ONE = from(1);
 
   /**
    * Creates a new {@link DD64bTraceId 64-bit TraceId} from the given {@code long} interpreted as
@@ -22,7 +22,7 @@ public interface DDTraceId {
    * @param id The {@code long} representing the bits of the unsigned 64-bit id.
    * @return A new {@link DDTraceId} instance.
    */
-  static DDTraceId from(long id) {
+  public static DDTraceId from(long id) {
     return DD64bTraceId.from(id);
   }
 
@@ -34,7 +34,7 @@ static DDTraceId from(long id) {
    * @return A new {@link DDTraceId} instance.
    * @throws NumberFormatException If the given {@link String} does not represent a valid number.
    */
-  static DDTraceId from(String s) throws NumberFormatException {
+  public static DDTraceId from(String s) throws NumberFormatException {
     return DD64bTraceId.create(LongStringUtils.parseUnsignedLong(s), s);
   }
 
@@ -47,7 +47,7 @@ static DDTraceId from(String s) throws NumberFormatException {
    * @throws NumberFormatException If the given {@link #toHexString() hexadecimal String} does not
    *     represent a valid number.
    */
-  static DDTraceId fromHex(String s) throws NumberFormatException {
+  public static DDTraceId fromHex(String s) throws NumberFormatException {
     if (s == null) {
       throw new NumberFormatException("s cannot be null");
     }
@@ -62,7 +62,7 @@ static DDTraceId fromHex(String s) throws NumberFormatException {
    *     instance.
    */
   @Override
-  String toString();
+  public abstract String toString();
 
   /**
    * Returns the lower-case zero-padded 32 hexadecimal characters {@link String} representation of
@@ -71,7 +71,7 @@ static DDTraceId fromHex(String s) throws NumberFormatException {
    * @return A cached lower-case zero-padded 32 hexadecimal characters {@link String} representation
    *     of the {@link DDTraceId} instance.
    */
-  String toHexString();
+  public abstract String toHexString();
 
   /**
    * Returns the lower-case zero-padded {@link #toHexString() hexadecimal String} representation of
@@ -83,15 +83,15 @@ static DDTraceId fromHex(String s) throws NumberFormatException {
    * @return A lower-case zero-padded {@link #toHexString() String representation} representation of
    *     the {@link DDTraceId} instance.
    */
-  String toHexStringPadded(int size);
+  public abstract String toHexStringPadded(int size);
 
   /**
    * Returns the low-order 64 bits of the {@link DDTraceId} as an unsigned {@code long}. This means
    * that values larger than {@link Long#MAX_VALUE} will be represented as negative numbers.
    *
    * @return The low-order 64 bits of the {@link DDTraceId} as an unsigned {@code long}.
    */
-  long toLong();
+  public abstract long toLong();
 
   /**
    * Returns the high-order 64 bits of 128-bit {@link DDTraceId} as un unsigned {@code long}. This
@@ -100,5 +100,5 @@ static DDTraceId fromHex(String s) throws NumberFormatException {
    * @return The high-order 64 bits of the 128-bit {@link DDTraceId} as an unsigned {@code long},
    *     <code>0</code> for 64-bit {@link DDTraceId} only.
    */
-  long toHighOrderLong();
+  public abstract long toHighOrderLong();
 }

dd-trace-api/src/test/groovy/datadog/trace/api/DDTraceIdTest.groovy

@@ -189,4 +189,14 @@ class DDTraceIdTest extends DDSpecification {
     // Too long id
     "1" * 33           | 0     | 33     | true
   }
+
+  def "check ZERO constant initialization"() {
+    when:
+    def zero = DDTraceId.ZERO
+    def fromZero = DDTraceId.from(0)
+
+    then:
+    zero != null
+    zero.is(fromZero)
+  }
 }

dd-trace-core/src/main/java/datadog/trace/core/propagation/B3TraceId.java

@@ -4,7 +4,7 @@
 import datadog.trace.api.DDTraceId;
 
 /** A B3 {@link DDTraceId} along with its original {@link String} representation. */
-public class B3TraceId implements DDTraceId {
+public class B3TraceId extends DDTraceId {
   /** The original {@link String} representation. */
   protected final String original;