隐式超级构造函数Person()未定义.必须显式调用另一个构造函数？

Question

我正在处理一个项目,我收到错误"隐式超级构造函数Person()未定义.必须显式调用另一个构造函数",我不太明白.

这是我的人类:

public class Person {
    public Person(String name, double DOB){

    }
}

我的学生班在尝试实现person类时,并给它一个教师变量.

public class Student extends Person {

    public Student(String Instructor) {

    }

}

Answer 1

如果构造函数未显式调用超类构造函数,则Java编译器会自动插入对超类的无参数构造函数的调用.

如果超类没有无参数构造函数,则会出现编译时错误.对象确实有这样的构造函数,因此如果Object是唯一的超类,则没有问题.

参考:http://docs.oracle.com/javase/tutorial/java/IandI/super.html :(参见"SubClass Constructors"部分)

因此,每当处理参数化构造函数时,都会 super(parameter1, parameter2 ..)调用父构造函数. 此super()调用也应该是构造函数块中的FIRST行.

Answer 2

您需要super调用已定义的构造函数:

public Student(String instructor) {
    super(/* name */, /* date of birth */);
}

你不能只是调用super()因为没有定义构造函数.

Answer 3

这就是我实现它的方式（在我的例子中，超类是 Team，子类是 Scorer）：

// Team.java
public class Team {
    String team;
    int won;
    int drawn;
    int lost;
    int goalsFor;
    int goalsAgainst;
    Team(String team, int won, int drawn, int lost, int goalsFor, int goalsAgainst){
        this.team = team;
        this.won = won;
        this.drawn = drawn;
        this.lost = lost;
        this.goalsFor = goalsFor;
        this.goalsAgainst = goalsAgainst;
    }
    int matchesPlayed(){
        return won + drawn + lost;
    }
    int goalDifference(){
        return goalsFor - goalsAgainst;
    }
    int points(){
        return (won * 3) + (drawn * 1);
    }
}
// Scorer.java
public class Scorer extends Team{
    String player;
    int goalsScored;
    Scorer(String player, int goalsScored, String team, int won, int drawn, int lost, int goalsFor, int goalsAgainst){
        super(team, won, drawn, lost, goalsFor, goalsAgainst);
        this.player = player;
        this.goalsScored = goalsScored;
    }
    float contribution(){
        return (float)this.goalsScored / (float)this.goalsFor;
    }
    float goalsPerMatch(){
        return (float)this.goalsScored/(float)(this.won + this.drawn + this.lost);
    }
}