consumer.How to specify partition to read? [kafka]

I am learning Kafka and I want to know how to specify the partition when I consume messages from a topic.

I have found several pictures like this:

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It means that a consumer can consume messages from several partitions but a partition can only be read by a single consumer (within a consumer group).

Also, I have read several examples for consumer and they look like this:

Properties props = new Properties();props.put("bootstrap.servers", "localhost:9092");props.put("group.id", "consumer-tutorial");props.put("key.deserializer", StringDeserializer.class.getName());props.put("value.deserializer", StringDeserializer.class.getName());KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props); 

and:

Subscribe:

consumer.subscribe(Arrays.asList(“foo”, “bar”)); 

Poll

 try {      while (running) {        ConsumerRecords<String, String> records = consumer.poll(1000);        for (ConsumerRecord<String, String> record : records)            System.out.println(record.offset() +": " + record.value());      } } finally {      consumer.close(); }

How does this work? From which partition will I read messages?