InMemoryTrollRepository.java

package javaapplication8;

import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Optional;

public class InMemoryTrollRepository {

    private final List<Troll> trolls = new LinkedList<>();

    public InMemoryTrollRepository() {
        Troll perceptroll = new Troll();
        perceptroll.setId(1L);
        perceptroll.setNick("perceptroll");
        trolls.add(perceptroll);
        
        Troll kyt = new Troll();
        kyt.setId(2L);
        kyt.setNick("kyt");
        trolls.add(kyt);
    }

    public List<Troll> list() {
        return Collections.unmodifiableList(trolls);
    }

    public int count() {
        return trolls.size();
    }

    public Optional<Troll> findById(Long id) {
        return trolls
                .stream()
                .filter((troll) -> troll.getId().equals(id))
                .findFirst();
   }
}

Troll.java

package javaapplication8;


public class Troll {
    private Long id;
    
    private String nick;
    
    private boolean hungry;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getNick() {
        return nick;
    }

    public void setNick(String nick) {
        this.nick = nick;
    }

    public boolean isHungry() {
        return hungry;
    }

    public void setHungry(boolean hungry) {
        this.hungry = hungry;
    }
    
    
}

TrollDetailForm

package javaapplication8;

import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import static javax.swing.BoxLayout.LINE_AXIS;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;


public class TrollDetailForm extends JFrame {
    
    private final InMemoryTrollRepository trollRepository = new InMemoryTrollRepository();
    
    private final JLabel trollLabel = new JLabel();
    
    public TrollDetailForm() {
        setLayout(new BoxLayout(getContentPane(), LINE_AXIS));
        
        initializeModel();
        
        trollLabel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
        add(trollLabel);
        
        setSize(800, 600);
        pack();
        
        setLocationRelativeTo(null);
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }
    
    private void initializeModel() {
        Troll troll = trollRepository.findById(2L).get();
        
        StringBuilder trollStatus = new StringBuilder("Troll ");
        trollStatus.append(troll.getNick());
        if(troll.isHungry()) {
            trollStatus.append(" needs food");
        } else {
            trollStatus.append(" needs food");
        }
        
        trollLabel.setText(trollStatus.toString());
    }
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new TrollDetailForm());
    }
}