[Java] Array of Varchar example is missleading

[Miro-Andrin]

import org.apache.arrow.memory.BufferAllocator;
import org.apache.arrow.memory.RootAllocator;
import org.apache.arrow.vector.VarCharVector;

try(
    BufferAllocator allocator = new RootAllocator();
    VarCharVector varCharVector = new VarCharVector("varCharVector", allocator);
) {
    varCharVector.allocateNew(3);
    varCharVector.set(0, "one".getBytes());
    varCharVector.set(1, "two".getBytes());
    varCharVector.set(2, "three".getBytes());
    varCharVector.setValueCount(3);

    System.out.print(varCharVector);
}

This snippet only works because few short strings are written. allocateNew does not grow the data buffer depending on the size of n (3 in this case). The example should either call the allocateNew method variant that specifies the byte count, use setSafe, or have a comment about this.

[amoeba]

Hi @Miro-Andrin, thanks for filing an issue.

The specifics about the various Java ValueVector routines are covered in the main docs at https://arrow.apache.org/docs/java/vector.html and I think they do a pretty good job as an introduction to these classes, including covering allocateNew and set/setSafe. The cookbooks (this repo) document common patterns that don't make sense in the primary docs and the code you shared is a common pattern.

Do you have an alternative approach you use often you'd like to add to the cookbook?