Java 子类化泛型参数

Question

如果之前有人问过这个问题，我很抱歉，但我真的不知道要搜索什么。

无论如何，我正在制作一个数学包，并且许多类都扩展了 Function:

package CustomMath;

@SuppressWarnings("rawtypes")
public abstract class Function <T extends Function> {

    public abstract Function getDerivative();

    public abstract String toString();

    public abstract Function simplify();

    public abstract boolean equals(T comparison);

}

我想比较函数以查看它们是否相等。如果它们来自同一个类，我想使用其特定的比较方法，但如果它们属于不同的类，我想返回 false。这是我目前的类(class)之一:

package CustomMath;

public class Product extends Function <Product> {

public Function multiplicand1;
public Function multiplicand2;

public Product(Function multiplicand1, Function multiplicand2)
{
    this.multiplicand1 = multiplicand1;
    this.multiplicand2 = multiplicand2;
}

public Function getDerivative() {
    return new Sum(new Product(multiplicand1, multiplicand2.getDerivative()), new Product(multiplicand2, multiplicand1.getDerivative()));
}

public String toString() {
    if(multiplicand1.equals(new RationalLong(-1, 1)))
        return String.format("-(%s)", multiplicand2.toString());
    return String.format("(%s)*(%s)", multiplicand1.toString(), multiplicand2.toString());
}

public Function simplify() {
    multiplicand1 = multiplicand1.simplify();
    multiplicand2 = multiplicand2.simplify();
    if(multiplicand1.equals(new One()))
        return multiplicand2;
    if(multiplicand2.equals(new One()))
        return multiplicand1;
    if(multiplicand1.equals(new Zero()) || multiplicand2.equals(new Zero()))
        return new Zero();
    if(multiplicand2.equals(new RationalLong(-1, 1))) //if one of the multiplicands is -1, make it first, so that we can print "-" instead of "-1"
    {
        if(!multiplicand1.equals(new RationalLong(-1, 1))) // if they're both -1, don't bother switching
        {
            Function temp = multiplicand1;
            multiplicand1 = multiplicand2;
            multiplicand2 = temp;
        }
    }
    return this;
}

public boolean equals(Product comparison) {
    if((multiplicand1.equals(comparison.multiplicand1) && multiplicand2.equals(comparison.multiplicand2)) || 
            (multiplicand1.equals(comparison.multiplicand2) && multiplicand2.equals(comparison.multiplicand1)))
        return true;
    return false;
}

}

我该怎么做？

Answer 1

使用泛型，您可以保证 equals 方法仅适用于类型“T”，在本例中为“Product”。您无法传递其他类类型。

另一种可能性是在类函数定义中:

public abstract boolean equals(Function comparison);

在 Product 类中，对象与 comparison instanceof Product 进行比较