为什么子类方法打印 null ？我究竟做错了什么？

Question

为什么我的代码将 null 作为输出值而不是传递的参数？

家长班级：

class Language{

  protected String name;

  protected int numSpeakers;

  protected String regionsSpoken;

  protected String wordOrder;

  

  public Language(String getName, int getNumSpeakers, String getRegionsSpoken, String getWordOrder){

    this.name = getName;

    this.numSpeakers = getNumSpeakers;

    this.regionsSpoken = getRegionsSpoken;

    this.wordOrder = getWordOrder;

  }

  

  public void getInfo(){

    System.out.println(name+ " is spoken by "+numSpeakers+"  people mainly in "+regionsSpoken);

    System.out.println("The language follows the word order: "+wordOrder);

  }

  

  public static void main(String[] args){

    Mayan mayanLanguage = new Mayan("Ki'che'",30000);

    mayanLanguage.getInfo();

  }

}

儿童班：

class Mayan extends Language {

  protected String name;

  protected int numSpeakers;

  

  Mayan(String languageName,int speakers ){

    super(languageName,speakers,"Central America","verb-object-subject");

  }

  

  @Override

  public void getInfo() {

    System.out.println(name+" is spoken by "+numSpeakers+" people mainly in Central America.");

    System.out.println("The language follows the word order: verb-object-subject");

    System.out.println("Fun fact: "+name+" is an ergative language.");

  }

}

我查看了代码并尝试通过更改来解决它，但似乎没有任何效果，我陷入了代码中没有看到的错误是什么。

预期是：

Ki'che' 有 2330000 人使用，主要分布在中美洲。该语言遵循词序：动词-宾语-主语 有趣的事实：Ki'che' 是一种作格语言。

实际是：

null 主要在中美洲有 0 人使用。该语言遵循词序：动词-宾语-主语 有趣的事实：null 是一种作格语言。

Answer 1

在Mayan你有领域protected String name;protected int numSpeakers;删除这些将解决您的问题。发生此问题的原因是因为当您定义上面的两行时，您隐藏了这两个字段，Language并且您必须从Languagelike super.name、super.numSpeakers等访问这些字段...您可能正在追求类似以下的内容。public class Mayan extends Language {    private static final String REGION = "Central America";    private static final String WORD_ORDER = "verb-object-subject";    public Mayan(String languageName, int speakers) {        super(languageName, speakers, REGION, WORD_ORDER);    }    @Override    public void getInfo() {        super.getInfo();        System.out.println("Fun fact: " + name + " is an ergative language.");    }}正如加文指出的，访问修饰符可以受到限制。如果您在程序的单个包中工作，您最终可能会得到类似的结果Language.javaclass Language {    String name;    private int numSpeakers;    private String regionsSpoken;    private String wordOrder;    Language(String getName, int getNumSpeakers, String getRegionsSpoken, String getWordOrder) {        this.name = getName;        this.numSpeakers = getNumSpeakers;        this.regionsSpoken = getRegionsSpoken;        this.wordOrder = getWordOrder;    }    void getInfo() {        System.out.println(name + " is spoken by " + numSpeakers + "  people mainly in " + regionsSpoken);        System.out.println("The language follows the word order: " + wordOrder);    }    public static void main(String[] args) {        Mayan mayanLanguage = new Mayan("Ki'che'",30000);        mayanLanguage.getInfo();    }}Mayan.javaclass Mayan extends Language {    private static final String REGION = "Central America";    private static final String WORD_ORDER = "verb-object-subject";    Mayan(String languageName, int speakers) {        super(languageName, speakers, REGION, WORD_ORDER);    }    @Override    void getInfo() {        super.getInfo();        System.out.println("Fun fact: " + name + " is an ergative language.");    }}