On Java Function interface implementation must use the final type of variable-CodePudding

I'm learning Java application of Stream, met such a problem:
For a given Student class, random 10 students, according to their grades group statistical proficiency, good rate and pass rate,
Student class implementation is as follows:

 
Public class Student implements Comparable {
private String id; 
private String name; 
Private String gender; 
private String dept; 
Private int score; 

Public Student () {}; 
Public Student (String id, String name, String gender, String dept, int score) {
this.id=id; 
this.name=name; 
This. Gender=gender; 
This. Dept=dept; 
This. Score=score; 
} 

Public String getId () {
return id; 
} 

Public String getName () {
return name; 
} 

Public String getDept () {
Return dept. 
} 
Public String getGender () {
Return the gender; 
} 

Public int getScore () {
Return score; 
} 

Public void showInfo () {
System. The out. Println (" student id: "+ id); 
System. The out. Println (" name: "+ name); 
System. The out. Println (" gender: "+ gender); 
System. The out. Println (", "professional + dept); 
System. The out. Println (" result: "+ score); 
System. The out. Println (" -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - "); 
} 

@ Override 
Public int compareTo (Student arg0) {
//Ordered by score desc 
Return arg0. Score - score; 
} 

}

I will student information reads coexist in an ArrayList

 
ArrayList Arrlist=new ArrayList<> (a);

Adopts the following method to generate the ArrayList of 10 different subscript, used for sampling

 
HashSet MySet=new HashSet (a); 
Int size=arrlist. The size (); 
While (MySet. The size ()!=10) {
MySet. Add ((int) (Math. The random () * (size - 1))); 
}

Now I want to by the stream on the 10 samples according to the group rules, rule is
- if grades & gt; Good=85
- else if grades & gt; Good=80
- else if grades & gt;=70 to pass the
- the else fail
I defined Map Number of Key significance is set, 0 means excellent group, good group 1, 2, said to pass the group, 3 failed the said group; The Value is the specific performance of each sample
I want to use the following ways to

 
Map TypeToScore=
MySet. Stream () 
The map (o1 - & gt; Arrlist. Get (o1). GetScore ()) 
Collect (Collectors. GroupingBy (o1 - & gt; {
If (o1 & gt; {
=85)return 0; 
} else if (o1 & gt; {
=80)return 1; 
} else if (o1 & gt; {
=70)return 2; 
} else {
Return 3; 
} 
}));

But doing so
when you make a mistake

 Local variable arrlist defined in an enclosing scope must be final or effectively final

I try not to use Lambda expressions, instead of an anonymous inner class, then switch to external to define new class to implement the Function interface, can appear the same error message,
Excuse me how to solve this problem?

CodePudding user response:

The
ArrayList Arrlist=new ArrayList<> (a);
Change
Final ArrayList Arrlist=new ArrayList<> (a);
Try
Because the lambda or anonymous classes using external local variables, the external local variables must be final,