添加时的java arraylist空指针异常 [英] java arraylist null pointer exception when adding

问题描述

有人可以帮助我理解为什么在添加到数组列表时为什么会得到空指针.我试图这样做，以便在单击按钮时更改按钮上的文本，但是我的 ArrayList 似乎没有在其中添加内容?

Could someone please help me understand why i'm getting a null pointer when adding to my array list. Im trying to make it so that it will change the text on a button when it is clicked, however my ArrayList does not seem to be adding the things into it?

public class Game {

private GUI gui;
private ArrayList<String> pairs;
boolean clicked; 

public Game() {
    gui = new GUI(this);
    clicked = false; 
    ArrayList<String> pairs = new ArrayList<String>();

}

public void addPairs() {
    pairs.add("dog"); // where i get the null pointer
    pairs.add("dog");
}

推荐答案

您正在阴影 Game 构造函数中的class字段 pairs .更改

You are shadowing the class field pairs in your Game constructor. Change

ArrayList<String> pairs = new ArrayList<String>();

到

pairs = new ArrayList<String>();

或，例如钻石运营商

pairs = new ArrayList<>();

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