[SPARK-52602] Document all public classes

### What changes were proposed in this pull request?

This PR aims to add a Javadoc to all public classes.

### Why are the changes needed?

To provide a proper documentation.

### Does this PR introduce _any_ user-facing change?

No behavior change because this is a Javadoc only change.

### How was this patch tested?

Pass the CIs.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #258 from dongjoon-hyun/SPARK-52602.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/BaseResource.java

@@ -27,6 +27,16 @@
 import org.apache.spark.k8s.operator.status.BaseState;
 import org.apache.spark.k8s.operator.status.BaseStatus;
 
+/**
+ * Base class for Spark Kubernetes Operator's custom resources like SparkApplication and
+ * SparkCluster.
+ *
+ * @param <S> The type of the state.
+ * @param <AS> The type of the attempt summary.
+ * @param <STATE> The type of the state.
+ * @param <SPEC> The type of the spec.
+ * @param <STATUS> The type of the status.
+ */
 public class BaseResource<
     S,
     AS extends BaseAttemptSummary,

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/Constants.java

@@ -19,6 +19,7 @@
 
 package org.apache.spark.k8s.operator;
 
+/** Constants used in the Spark Kubernetes Operator. */
 @SuppressWarnings("PMD.DataClass")
 public class Constants {
   public static final String API_GROUP = "spark.apache.org";

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/SparkApplication.java

@@ -32,6 +32,7 @@
 import org.apache.spark.k8s.operator.status.ApplicationStateSummary;
 import org.apache.spark.k8s.operator.status.ApplicationStatus;
 
+/** SparkApplication is the Custom Resource Definition (CRD) for a Spark application. */
 @JsonInclude(JsonInclude.Include.NON_NULL)
 @JsonDeserialize()
 @Group(Constants.API_GROUP)

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/SparkApplicationList.java

@@ -22,5 +22,6 @@
 import io.fabric8.kubernetes.api.model.DefaultKubernetesResourceList;
 import lombok.NoArgsConstructor;
 
+/** List of SparkApplications. */
 @NoArgsConstructor
 public class SparkApplicationList extends DefaultKubernetesResourceList<SparkApplication> {}

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/SparkCluster.java

@@ -32,6 +32,7 @@
 import org.apache.spark.k8s.operator.status.ClusterStateSummary;
 import org.apache.spark.k8s.operator.status.ClusterStatus;
 
+/** SparkCluster is the Custom Resource Definition (CRD) for a Spark cluster. */
 @JsonInclude(JsonInclude.Include.NON_NULL)
 @JsonDeserialize()
 @Group(Constants.API_GROUP)

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/SparkClusterList.java

@@ -22,5 +22,6 @@
 import io.fabric8.kubernetes.api.model.DefaultKubernetesResourceList;
 import lombok.NoArgsConstructor;
 
+/** List of SparkClusters. */
 @NoArgsConstructor
 public class SparkClusterList extends DefaultKubernetesResourceList<SparkCluster> {}

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/spec/ApplicationSpec.java

@@ -31,6 +31,7 @@
 import lombok.EqualsAndHashCode;
 import lombok.NoArgsConstructor;
 
+/** Spec for a Spark application. */
 @Data
 @NoArgsConstructor
 @AllArgsConstructor

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/spec/ApplicationTimeoutConfig.java

@@ -26,6 +26,7 @@
 import lombok.Data;
 import lombok.NoArgsConstructor;
 
+/** Application timeout configuration. */
 @Data
 @NoArgsConstructor
 @AllArgsConstructor

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/spec/ApplicationTolerations.java

@@ -26,6 +26,7 @@
 import lombok.Data;
 import lombok.NoArgsConstructor;
 
+/** Toleration settings for a Spark application. */
 @Data
 @NoArgsConstructor
 @AllArgsConstructor

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/spec/BaseApplicationTemplateSpec.java

@@ -27,6 +27,7 @@
 import lombok.Data;
 import lombok.NoArgsConstructor;
 
+/** Base class for application template specs for driver and executors. */
 @Data
 @NoArgsConstructor
 @AllArgsConstructor