an installer

package net.pulchraprospectus.installer;

public class InstallerCallback {
    private final InstallerFrame callbackFrame;
    private final InstallerCallback.ListenerType type;

    public InstallerCallback (InstallerFrame frame, Installer installer, InstallerCallback.ListenerType listenerType) {
        this.callbackFrame = frame;
        this.type = listenerType;
        installer.addCallbackListener(this);
    }

    public void installerEventFired (InstallerEvent event) {
        if (this.type.test(event)) {
            this.type.onEvent(event);
        }
    }

    public static class ListenerType implements Predicate {
        public static final ListenerType VERIFY_LISTENER = new ListenerType(Installer::staticOnVerify, "Verify Listener");
        public static final ListenerType DOWNLOAD_LISTENER = new ListenerType(Installer::staticOnDownload, "Download Listener");
        public static final ListenerType UNPACK_LISTENER = new ListenerType(Installer::staticOnUnpack, "Unpack Listener");
        public static final ListenerType BACKUP_LISTENER = new ListenerType(Installer::staticOnBackup, "Backup Listener");
        public static final ListenerType INSTALL_LISTENER = new ListenerType(Installer::staticOnInstall, "Install Listener");

        private final Consumer<InstallerEvent> function;
        private final String name;

        public ListenerType (Consumer<InstallerEvent> trigger, String title) {
            this.function = trigger;
            this.predicate = predicate;
            this.name = title;
        }

        public boolean test (InstallerEvent event) {
            return event.getListenerType().getName() == this.getName();
        }

        public void onEvent (InstallerEvent event) {
            this.function.accept(event);
        }
    }
}

package net.pulchraprospectus.installer;

public class Installer {
    public Installer (File installDirectory) {
        if (instance != null) {
            this = instance;
        } else {
            this.dir = installDirectory;
        }
    }

    public Installer setCallback (InstallerCallback callback) {
        this.callback = callback;
        return this;
    }

    public Installer getInstance () {
        return instance;
    }

    static void setInstance (Installer installer) {
        if (!installer.file.exists() || !installer.file.isDirectory() || !Verifier.verifyMinecraftIntegrity(installer.file) || !Verifier.verifyForgeIntegrity(installer.file)) throw new java.nio.file.FileSystemNotFoundException("Minecraft directory not present, or is not a directory.");
        else {
            instance = installer;
        }
    }
}