Minor fixes to DiskInfo and configuration

- Add required fields to Builder constructors
- Remove redundant checkNotNull
- Better document sizeGb and diskType setters

gcloud-java-compute/src/main/java/com/google/gcloud/compute/DiskConfiguration.java

@@ -109,7 +109,7 @@ public B sizeGb(Long sizeGb) {
     }
 
     /**
-     * Sets the identity of the disk type.
+     * Sets the identity of the disk type. If not set {@code pd-standard} will be used.
      */
     public B diskType(DiskTypeId diskType) {
       this.diskType = diskType;

gcloud-java-compute/src/main/java/com/google/gcloud/compute/DiskInfo.java

@@ -147,7 +147,10 @@ static final class BuilderImpl extends Builder {
     private Long lastAttachTimestamp;
     private Long lastDetachTimestamp;
 
-    BuilderImpl() {}
+    BuilderImpl(DiskId diskId, DiskConfiguration configuration) {
+      this.diskId = checkNotNull(diskId);
+      this.configuration = checkNotNull(configuration);
+    }
 
     BuilderImpl(DiskInfo diskInfo) {
       this.id = diskInfo.id;
@@ -258,10 +261,10 @@ public DiskInfo build() {
 
   DiskInfo(BuilderImpl builder) {
     this.id = builder.id;
-    this.configuration = checkNotNull(builder.configuration);
+    this.configuration = builder.configuration;
     this.creationTimestamp = builder.creationTimestamp;
     this.creationStatus = builder.creationStatus;
-    this.diskId = checkNotNull(builder.diskId);
+    this.diskId = builder.diskId;
     this.description = builder.description;
     this.licenses = builder.licenses;
     this.attachedInstances = builder.attachedInstances;
@@ -383,7 +386,7 @@ public boolean equals(Object obj) {
    * {@link ImageDiskConfiguration} to create a disk from a disk image.
    */
   public static Builder builder(DiskId diskId, DiskConfiguration configuration) {
-    return new BuilderImpl().diskId(diskId).configuration(configuration);
+    return new BuilderImpl(diskId, configuration);
   }
 
   /**

gcloud-java-compute/src/main/java/com/google/gcloud/compute/ImageDiskConfiguration.java

@@ -44,8 +44,9 @@ public static class Builder
     private ImageId sourceImage;
     private String sourceImageId;
 
-    private Builder() {
+    private Builder(ImageId sourceImage) {
       super(Type.IMAGE);
+      this.sourceImage = checkNotNull(sourceImage);
     }
 
     private Builder(ImageDiskConfiguration configuration) {
@@ -60,6 +61,17 @@ private Builder(Disk diskPb) {
       this.sourceImageId = diskPb.getSourceImageId();
     }
 
+    /**
+     * Sets the size of the persistent disk, in GB. If not set the disk will have the size of the
+     * image. This value can be larger than the image's size. If the provided size is smaller than
+     * the image's size then disk creation will fail.
+     */
+    @Override
+    public Builder sizeGb(Long sizeGb) {
+      super.sizeGb(sizeGb);
+      return this;
+    }
+
     /**
      * Sets the identity of the source image used to create the disk.
      */
@@ -84,7 +96,7 @@ public ImageDiskConfiguration build() {
 
   private ImageDiskConfiguration(Builder builder) {
     super(builder);
-    this.sourceImage = checkNotNull(builder.sourceImage);
+    this.sourceImage = builder.sourceImage;
     this.sourceImageId = builder.sourceImageId;
   }
 
@@ -145,7 +157,7 @@ Disk toPb() {
    * Returns a builder for an {@code ImageDiskConfiguration} object given the image identity.
    */
   public static Builder builder(ImageId imageId) {
-    return new Builder().sourceImage(imageId);
+    return new Builder(imageId);
   }
 
   /**

gcloud-java-compute/src/main/java/com/google/gcloud/compute/SnapshotDiskConfiguration.java

@@ -45,8 +45,9 @@ public static class Builder
     private SnapshotId sourceSnapshot;
     private String sourceSnapshotId;
 
-    private Builder() {
+    private Builder(SnapshotId sourceSnapshot) {
       super(Type.SNAPSHOT);
+      this.sourceSnapshot = checkNotNull(sourceSnapshot);
     }
 
     private Builder(SnapshotDiskConfiguration configuration) {
@@ -61,6 +62,21 @@ private Builder(Disk diskPb) {
       this.sourceSnapshotId = diskPb.getSourceSnapshotId();
     }
 
+    /**
+     * Sets the size of the persistent disk, in GB. If not set the disk will have the size of the
+     * snapshot. This value can be larger than the snapshot's size. If the provided size is smaller
+     * than the snapshot's size then disk creation will fail.
+     *
+     * @see <a href="
+     *     https://cloud.google.com/compute/docs/disks/persistent-disks#restoresnapshotlargersize">
+     *     Restoring a snapshot to a larger size</a>
+     */
+    @Override
+    public Builder sizeGb(Long sizeGb) {
+      super.sizeGb(sizeGb);
+      return this;
+    }
+
     /**
      * Sets the identity of the source snapshot used to create the disk.
      */
@@ -85,7 +101,7 @@ public SnapshotDiskConfiguration build() {
 
   private SnapshotDiskConfiguration(Builder builder) {
     super(builder);
-    this.sourceSnapshot = checkNotNull(builder.sourceSnapshot);
+    this.sourceSnapshot = builder.sourceSnapshot;
     this.sourceSnapshotId = builder.sourceSnapshotId;
   }
 
@@ -148,7 +164,7 @@ Disk toPb() {
    * Returns a builder for a {@code SnapshotDiskConfiguration} object given the snapshot identity.
    */
   public static Builder builder(SnapshotId sourceSnapshot) {
-    return new Builder().sourceSnapshot(sourceSnapshot);
+    return new Builder(sourceSnapshot);
   }
 
   /**

gcloud-java-compute/src/main/java/com/google/gcloud/compute/StandardDiskConfiguration.java

@@ -48,6 +48,15 @@ private Builder(Disk diskPb) {
       super(Type.STANDARD, diskPb);
     }
 
+    /**
+     * Sets the size of the persistent disk, in GB. If not set, 500GB is used.
+     */
+    @Override
+    public Builder sizeGb(Long sizeGb) {
+      super.sizeGb(sizeGb);
+      return this;
+    }
+
     /**
      * Creates a {@code StandardDiskConfiguration} object.
      */