Add @Nullable to the parameter of equals(Object) (#2093)

Motivation:

`Object.equals(Object)` accepts `null`, but many of our `equals()`
implementations do not have `@Nullable` annotation on their parameters.

Modifications:

- Add `@Nullable` to the parameter of `equals(Object)`

Result:

- Better `null`-related inference

Author: trustin

CONTRIBUTING.md

@@ -212,7 +212,7 @@ public final class MyClass {
     }
 
     @Override
-    public boolean equals(Object obj) {
+    public boolean equals(@Nullable Object obj) {
         ... usual type check ...
         // OK
         return name.equals(((MyClass) obj).name);

core/src/main/java/com/linecorp/armeria/client/ClientDecoration.java

@@ -20,6 +20,8 @@
 import java.util.List;
 import java.util.function.Function;
 
+import javax.annotation.Nullable;
+
 import com.linecorp.armeria.common.Request;
 import com.linecorp.armeria.common.Response;
 
@@ -113,7 +115,7 @@ Function<Client<I, O>, Client<I, O>> decorator() {
         }
 
         @Override
-        public boolean equals(Object o) {
+        public boolean equals(@Nullable Object o) {
             if (this == o) {
                 return true;
             }

core/src/main/java/com/linecorp/armeria/client/DefaultEventLoopScheduler.java

@@ -29,6 +29,8 @@
 import java.util.concurrent.atomic.AtomicLongFieldUpdater;
 import java.util.function.ToIntFunction;
 
+import javax.annotation.Nullable;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -262,7 +264,7 @@ public int hashCode() {
         }
 
         @Override
-        public boolean equals(Object obj) {
+        public boolean equals(@Nullable Object obj) {
             if (this == obj) {
                 return true;
             }

core/src/main/java/com/linecorp/armeria/client/Endpoint.java

@@ -643,7 +643,7 @@ private static void validateWeight(int weight) {
     }
 
     @Override
-    public boolean equals(Object obj) {
+    public boolean equals(@Nullable Object obj) {
         if (this == obj) {
             return true;
         }

core/src/main/java/com/linecorp/armeria/client/HttpChannelPool.java

@@ -551,7 +551,7 @@ static final class PoolKey {
         }
 
         @Override
-        public boolean equals(Object o) {
+        public boolean equals(@Nullable Object o) {
             if (this == o) {
                 return true;
             }

core/src/main/java/com/linecorp/armeria/client/circuitbreaker/EventCount.java

@@ -16,6 +16,8 @@
 
 package com.linecorp.armeria.client.circuitbreaker;
 
+import javax.annotation.Nullable;
+
 /**
  * An immutable object that stores the count of events.
  */
@@ -99,7 +101,7 @@ public int hashCode() {
     }
 
     @Override
-    public boolean equals(Object o) {
+    public boolean equals(@Nullable Object o) {
         if (this == o) {
             return true;
         }

core/src/main/java/com/linecorp/armeria/client/endpoint/dns/DnsQuestionWithoutTrailingDot.java

@@ -19,6 +19,8 @@
 
 import java.net.IDN;
 
+import javax.annotation.Nullable;
+
 import io.netty.handler.codec.dns.DnsQuestion;
 import io.netty.handler.codec.dns.DnsRecordType;
 
@@ -56,7 +58,7 @@ public long timeToLive() {
     }
 
     @Override
-    public boolean equals(Object o) {
+    public boolean equals(@Nullable Object o) {
         if (this == o) {
             return true;
         }

core/src/main/java/com/linecorp/armeria/common/AbstractHttpData.java

@@ -16,6 +16,8 @@
 
 package com.linecorp.armeria.common;
 
+import javax.annotation.Nullable;
+
 /**
  * Support APIs for creating well-behaved {@link HttpData} objects. {@link HttpData} generally should extend
  * {@link AbstractHttpData} to interact with other {@link HttpData} implementations, via, e.g., {@code equals}.
@@ -37,7 +39,7 @@ public int hashCode() {
     }
 
     @Override
-    public boolean equals(Object obj) {
+    public boolean equals(@Nullable Object obj) {
         if (!(obj instanceof AbstractHttpData)) {
             return false;
         }

core/src/main/java/com/linecorp/armeria/common/AbstractRequestContext.java

@@ -26,6 +26,8 @@
 import java.util.function.Consumer;
 import java.util.function.Function;
 
+import javax.annotation.Nullable;
+
 import com.linecorp.armeria.common.util.SafeCloseable;
 import com.linecorp.armeria.server.DefaultServiceRequestContext;
 
@@ -195,7 +197,7 @@ public final int hashCode() {
     }
 
     @Override
-    public final boolean equals(Object obj) {
+    public final boolean equals(@Nullable Object obj) {
         return super.equals(obj);
     }
 }

core/src/main/java/com/linecorp/armeria/common/CacheControl.java

@@ -15,6 +15,8 @@
  */
 package com.linecorp.armeria.common;
 
+import javax.annotation.Nullable;
+
 /**
  * Directives for HTTP caching mechanisms in requests or responses. Use {@link ServerCacheControl} for
  * response-side and {@link ClientCacheControl} for request-side.
@@ -115,7 +117,7 @@ final StringBuilder newHeaderValueBuffer() {
     }
 
     @Override
-    public boolean equals(Object o) {
+    public boolean equals(@Nullable Object o) {
         if (this == o) {
             return true;
         }