How to do for every time you pass "true", it print the entire instantiated object?

Question

import java.util.ArrayList;

public class Loja {

    private ArrayList<Produto> ListaDeProdutos = new ArrayList<>();

    public void cadastrarProduto(Produto produto){
        ListaDeProdutos.add(produto);
    }

    public void listarProdutos(){
        ListaDeProdutos.forEach(P -> System.out.println(P.toString() + "\n"));
    }

    public void listarDiscos(){
        ListaDeProdutos.forEach(P -> System.out.println(P.toString().contains("Banda"))); 
        //eu quero que ele imprima todo o conteúdo setado, não apenas "true"
    }
}

Testing

public class Teste {
    public static void main(String[] args) {
        Loja l1 = new Loja();
        l1.cadastrarProduto(new Livro("Java - Use A cabeça", 01, 120.00f, "Fulano de tal", "DevMasters", 400, "PROGRAMAÇÃO"));
        l1.cadastrarProduto(new Livro("LIVRO DE C", 02, 80.00f, "Deitel", "Dev Masters", 800, "PROGRAMAÇÃO"));
        l1.cadastrarProduto(new Livro("PYTHON", 03, 100.00f, "Lokão dazideia", "Dev Masters", 200, "PROGRAMAÇÃO"));
        l1.cadastrarProduto(new Disco("Back in Black", 04, 100.00f, "AC/DC", "Hard Rock", 15));
        l1.cadastrarProduto(new Disco("Sattelite", 05, 20.00f, "P.O.D.", "White Metal", 11));
        l1.cadastrarProduto(new Disco("Musashi", 06, 15.00f, "Rashid", "Rap", 14));    
        l1.listarDiscos();
    }
}

Exit

false
false
false
true
true
true

Answer 1

The question does not give many details, but it would be something like this:

for (Produto produto : ListaDeProdutos ) {
    if (produto.nome.contains("Banda")) {
        System.out.println(produto.nome);
        System.out.println(produto.preco);
        System.out.println(produto.genero);
    }
}

I put in the Github for future reference.

I thought better to do. The use of stream may seem cute, but it is slower, has semantics different from the normal loop, although in this example does not cause problems, but has a number of implications that almost nobody understands and the normal is to cause problems, and there is almost always no real gain except, in some cases, leave a code with fewer lines, which is not always good. In which case it wouldn’t actually happen, so it’s just a waste of time.

Also don’t use the tostring() for that reason, it makes no sense to create something of general logic to meet a specific requirement. It is an abuse to use it to format data, even worse to have a debugging function used with complexity O(n).

Actually there may be a conceptual error there. I don’t know if Loja should print something, it process is ok, print is already a platform detail where it runs and maybe should be manipulated elsewhere. For exercise you can do so, but know that in real code is not how you do it.

Answer 2

The method contains returns a boolean, so the code only prints true or false. If you want to print products that meet a condition, you can make a for simple as suggested by Maniero.

Another option is to turn the list into one stream and use filter to filter the products that satisfy their condition and then print them:

ListaDeProdutos.stream()
    // filtrar produtos
    .filter(p -> p.toString().contains("Banda"))
    // imprimir
    .forEach(System.out::println);

But if you want to filter the products by a specific type (in case, Disco), could use instanceof to test whether the product is an instance of Disco:

ListaDeProdutos.stream()
    // filtrar produtos que são Disco
    .filter(p -> p instanceof Disco)
    // imprimir
    .forEach(System.out::println);