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Charismatic
Asked:2022-06-20 17:02:14 +0000 UTC2022-06-20 17:02:14 +0000 UTC

Java泛型的比较

  • 772
public class Student<NU,N,A,R,O> {
    private final NU nu;
    private final N n;
    private final A a;
    private final R r;
    private final O o;

    public Student(NU nu, N n, A a, R r, O o) {
        this.nu = nu;
        this.n = n;
        this.a = a;
        this.r = r;
        this.o = o;
    }

    public N getN() {
        return n;
    }
    public A getA() {
        return a;
    }
    public R getR() {
        return r;
    }

    @Override
    public String toString() {
        return "\n Student[" +
                "Порядковый номер = " + nu +
                ", Имя = '" + n + '\'' +
                ", Возраст = " + a +
                ", Оценка = " + r +
                ", Олимпядник = " + o +
                ']' ;
    }
}

COMPARATOR 
public class StudentsComparatorsAgeAndRating implements Comparator<Student<Integer,String,Integer,Double,Boolean>> {

    @Override
    public int compare(Student o1, Student o2) {
        if (!(o1.getA().equals(o2))) {
            return (Integer)o1.getA() - (Integer)o2.getA();
        }
        return 0;
    }
}
public class StudentsComparatorsName implements Comparator<Student<Integer, String, Integer, Double, Boolean>> {

    @Override
    public int compare(Student o1, Student o2) {
        return (Integer)o1.getN().toString().length() - (Integer) o2.getN().toString().length();
    }
}
public class StudentsComparatorsRating implements Comparator<Student<Integer, String, Integer, Double, Boolean>> {
    @Override
    public int compare(Student o1, Student o2) {
        BigDecimal bd = BigDecimal.valueOf((Double)o1.getR());
        BigDecimal bd1 = BigDecimal.valueOf((Double)o2.getR());
        return bd1.compareTo(bd);
    }
}

问题是，我可以在没有类型转换的情况下比较泛型吗？

java

1 个回答

  1. Best Answer

    为了避免比较器类中的类型转换，您应该在这些类中指定完整类型：

    class StudentsComparatorsAgeAndRating implements Comparator<Student<Integer,String,Integer,Double,Boolean>> {

    @Override
    public int compare(
        Student<Integer,String,Integer,Double,Boolean> o1, 
        Student<Integer,String,Integer,Double,Boolean> o2
    ) {
        if (!(o1.getA().equals(o2))) {
            return o1.getA() - o2.getA();
        }
        return 0;
    }
}

    因为当使用public int compare(Student o1, Student o2)没有指定特定类的方法时，编译器不会“理解”哪个类将用于 fields Student。

    摆脱对比较器不必要的冗长描述的另一种方法是创建一个具有类型规范和构造函数的类，并为这样的类创建比较器：

    class MyStudent extends Student<Integer,String,Integer,Double,Boolean> {
    public MyStudent(Integer id, String name, Integer age, Double rating, Boolean olympic) {
        super(id, name, age, rating, olympic);
    }
}

class MyStudentComparators {
    public static Comparator<MyStudent> byAge = Comparator.comparingInt(MyStudent::getA);
    public static Comparator<MyStudent> byAgeAndRating = byAge.thenComparingDouble(MyStudent::getR);
    public static Comparator<MyStudent> byName = Comparator.comparing(MyStudent::getN);
    public static Comparator<MyStudent> byNameLength = Comparator.comparingInt(ms -> ms.getN().length());
}
    • 1

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