How is the joy of friendship portrayed in Boyne's The Boy in the Striped Pajamas?

In Boyne's The Boy in the Striped Pajamas, Bruno is a typical boy who loves to play with his friends. His best friends in Berlin are Karl, Daniel, and Martin. What Bruno finds most joyful with these friends can be described in the plans he wants to fulfill in the following passage:

[The plans] included causing a lot of chaos, especially in a few weeks' time when school finished for the summer holidays and they didn't have to spend all their time just making plans but could actually put them into effect instead (8).

Unfortunately, Bruno must move with his parents to Auschwitz, and he becomes lonely without his friends. Bruno finds joy in a new companionship when he meets Shmuel, who lives in the concentration camp there. The friendship is different, however, because he can't make the same plans with Shmuel as he did with his other friends. Therefore, Bruno and Shmuel find joy in their friendship in non-traditional ways. First, they make plans to meet on certain days by the fence to talk. They may not get to play ball or tag with each other, but these meetings give each of them something to look forward to. They also bear each other's burdens by listening to each other. Bruno explains his friendship with Shmuel to his sister as though he had an imaginary friend, but the joy of it comes through as follows:

We talk about everything. . . I tell him about our house back in Berlin and all the other houses and the streets and the fruit and vegetable stalls and the cafes. . . and about Karl and Daniel and Martin and how they were my three best friends for life. . . He tells me about his family and the watch shop that he used to live over and the adventures he had coming here and the friends he used to have (157-158).

Even though the two boys don't have a way to play games together, they do find peace and joy confiding in each other. When the boys finally decide to dress Bruno up in "pajamas" so he can help Shmuel look for his father, both become excited, as shown in the following passage:

Both boys went home in high spirits that afternoon. Bruno imagined a great adventure ahead and finally an opportunity to see what was really on the other side of the fence before he went back to Berlin. . . and Shmuel saw a chance to get someone to help him in the search for his papa (199).

Finally, the boys both feel joy at a chance to be together on one side of the fence. Unfortunately, they die together in a gas chamber, but at least they first experience the joy of friendship during a very difficult time in their lives.