另一个类的子类的Java Getting属性

Question

我在动作侦听器中设置超类属性arraylist Pokemon pokeSlots“>

问题：我希望能够实例化另一个类中的子类（HumanTrainer）的实例，并在用于人类训练器的pokeslot中访问口袋妖怪，但我一直无法弄清楚该如何做。任何尝试都只是返回一个空数组或nullpointerexception。

 btnSelect.addActionListener(e -> {
            //allows you select and remove multiple pokemon at the same time by returning arrays
            if(maxPokemon<2) {
                //get the selected element's index and value. 
                Object[] lstValues = lstDisplayAllPokemon.getSelectedValuesList().toArray();
                int[] lstIndices = lstDisplayAllPokemon.getSelectedIndices();

                for (int i = 0; i < lstIndices.length; i++) {
                    //need to get Pokemon from pokemonlist where lstIndices[i] and store in selectedPokemonList
                    selectedPokemonList.add(pokemonList.get(lstIndices[i]));
                    new HumanTrainer(selectedPokemonList);
                    model1.setElementAt(lstValues[i] + " (Selected)", lstIndices[i]);
                    maxPokemon++;
                }
            }
        });
超类

import java.util.ArrayList;

abstract public class Trainer{
    protected String name;
    protected ArrayList<Pokemon> pokeSlots;
    protected ArrayList<Item> items;
}
子类

import java.util.ArrayList;

public class HumanTrainer extends Trainer{
    int money;
    //private ArrayList<Pokemon> pokeSlots;

    HumanTrainer(){

    }
    HumanTrainer(ArrayList<Pokemon> pPokemon){
        this.pokeSlots = pPokemon;
        for (Pokemon ps: pPokemon) {
            System.out.println(ps.name);
        }
    }
}
其他类别

Trainer Human = new HumanTrainer();
Human.pokeSlots.get(0);
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at BattleGUI.DefaultBattleMenu(BattleGUI.java:138)
    at BattleGUI.<init>(BattleGUI.java:40)
    at MainMenuGUI.lambda$new$2(MainMenuGUI.java:171)
    at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967)
    at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308)
    at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
    at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
    at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279)
    at java.desktop/java.awt.Component.processMouseEvent(Component.java:6636)
    at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342)
    at java.desktop/java.awt.Component.processEvent(Component.java:6401)
    at java.desktop/java.awt.Container.processEvent(Container.java:2263)
    at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5012)
    at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2321)
    at java.desktop/java.awt.Component.dispatchEvent(Component.java:4844)
    at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4919)
    at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4548)
    at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4489)
    at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2307)
    at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2764)
    at java.desktop/java.awt.Component.dispatchEvent(Component.java:4844)
    at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772)
    at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
    at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95)
    at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
    at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
    at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
    at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
    at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
    at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
    at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
    at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

我正在动作侦听器中设置超类属性arraylist Pokemon pokeSlots“问题：我希望能够实例化另一个类中的子类（HumanTrainer）的实例，并且...]]

Answer 1

您只需创建一个新对象并将其丢弃。使用参考并使用它。