英文:
Is it possible for Java interface with generics to enforce the generic type?
问题
考虑这个例子
public interface Equatable<T> {
public boolean equal(T t1, T t2);
}
public class Square implements Equatable<Square> {
public boolean equal(Square t1, Square t2) {
return false;
}
}
接口Equatable是否可以强制Square实现一个接受两个Square对象作为参数的equal函数，而不仅仅是两个任意类型的对象（例如两个字符串等）？
英文:
Consider this example
public interface Equatable<T> {
public boolean equal(T t1, T t2);
}
public class Square implements Equatable<Square> {
public boolean equal(Square t1, Square t2) {
return false;
}
}
Is it possible for the interface Equatable to enforce Square to implement an equal function that takes in two Squares, and not just two of any types (two Strings etc)?
答案1
得分: 1
是的，你没有定义接口中的 "T" 是什么，你可以将其限制为只能用于实现 Equatable 接口的类，因此 String 将不被允许：
public interface Equatable<T extends Equatable<T>>
{
//...
}
正确的用法：
public class Square implements Equatable<Square>
{
public boolean equal(Square t1, Square t2)
{
return false;
}
}
编译错误：
public class Circle implements Equatable<String>
{
public boolean equal(String t1, String t2)
{
return false;
}
}
注意：
请注意，将相同的类型名称放入尖括号中是你的责任，因为编译器不会覆盖下面的情况。
我猜你想阻止对不同类型使用 equal 方法。
public class Square implements Equatable<Circle>
{
public boolean equal(Circle t1, Circle t2)
{
return false;
}
}
英文:
Yes, you didn't define what is "T" in your interface, you can limit it only to classes which implements Equatable, so String will not be allowed:
public interface Equatable<T extends Equatable<T>>
{
//...
}
Works Good:
public class Square implements Equatable<Square>
{
public boolean equal(Square t1, Square t2)
{
return false;
}
}
Compilation Error:
public class Circle implements Equatable<String>
{
public boolean equal(String t1, String t2)
{
return false;
}
}
Note<br>
Pay attention, it's your responsibility to put in the brackets the same Type name, because below case will not be covered by compiler.<br>
I guess you want to disallow to use equal method for different type.
public class Square implements Equatable<Circle>
{
public boolean equal(Circle t1, Circle t2)
{
return false;
}
}
答案2
得分: 0
你可以通过递归的泛型类型在一定程度上实现这一点。
public interface Equatable<T extends Equatable<T>> {
public boolean equal(T t1, T t2);
}
相关链接：https://stackoverflow.com/questions/211143/java-enum-definition
英文:
You can enforce this to an extent with a recursive generic type.
public interface Equatable<T extends Equatable<T>> {
public boolean equal(T t1, T t2);
}
related: https://stackoverflow.com/questions/211143/java-enum-definition
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