在该类的方法体内实例化一个泛型类

Question

我试图在该类的一个方法内实例化一个泛型类，但有编译时错误。希望有人能提供一些见解这里：

//returns a new ILo<T> with all items in this list that satisfy 
//the given predicate 
public ILo<T> filter(ISelect<T> pred); 


// Represents a nonempty list of items of type T 
class ConsLo<T> implements ILo<T>{ 
    T first; 
    ILo<T> rest; 


//returns a new ILo<T> with all items in this list that satisfy 
//the given predicat 
public ILo<T> filter(ISelect pred) { 
    return new ConsLo<T>(pred.select(this.first), 
      this.rest.filter(pred)); 
} 

我提供方法的接口定义，其次是ConsLo类的定义，然后由我处理方法声明。我不明白我如何在保留泛型的同时实例化这个类，以便处理任何类型和谓词pred。以下是编译器错误：

ILo.java:95: error: method select in interface ISelect<T#3> cannot be applied to given types; 
return new ConsLo<T>(pred.select(this.first), 
         ^
required: T#1 
found: T#2 
reason: actual argument T#2 cannot be converted to T#1 by method invocation conversion 
where T#1,T#2,T#3 are type-variables: 
T#1 extends Object declared in method <T#1>filter(ISelect<T#1>) 
T#2 extends Object declared in class ConsLo 
T#3 extends Object declared in interface ISelect 

Answer 1

您应该使用的ISelect通用版：

public ILo<T> filter(ISelect<T> pred) { 
    return new ConsLo<T>(pred.select(this.first), 
     this.rest.filter(pred)); 
} 

这样pred将ISelect<T>，而不是I选择 - 这是两种类型T#1和T#2编译器抱怨关于。