Fix remaining compiler warnings

Fix remaining Java compiler warnings, mainly around missing
generics or deprecated code.

Also add the `-Werror` compiler option to ensure that any future
warnings will fail the build.

Issue: SPR-11064

spring-aop/src/test/java/org/springframework/tests/aop/interceptor/NopInterceptor.java

@@ -46,6 +46,11 @@ public class NopInterceptor implements MethodInterceptor {
 		++count;
 	}
 
+	@Override
+	public int hashCode() {
+		return 0;
+	}
+
 	@Override
 	public boolean equals(Object other) {
 		if (!(other instanceof NopInterceptor)) {
@@ -57,4 +62,5 @@ public class NopInterceptor implements MethodInterceptor {
 		return this.count == ((NopInterceptor) other).count;
 	}
 
+
 }

spring-aop/src/test/java/org/springframework/tests/sample/beans/SerializablePerson.java

@@ -28,7 +28,11 @@ import org.springframework.util.ObjectUtils;
 @SuppressWarnings("serial")
 public class SerializablePerson implements Person, Serializable {
 
+	private static final long serialVersionUID = 1L;
+
+
 	private String name;
+
 	private int age;
 
 	@Override
@@ -59,6 +63,11 @@ public class SerializablePerson implements Person, Serializable {
 		return o;
 	}
 
+	@Override
+	public int hashCode() {
+		return 0;
+	}
+
 	@Override
 	public boolean equals(Object other) {
 		if (!(other instanceof SerializablePerson)) {