The type of the expression must be an array type b

问题:

I hit a bump when I'm doing my Java code. I feel like I somehow got the concept messed up, like I not sure for this:

void setScore(float[] sco)
{
    sco = score;
}

public void setScore(float sco, int id)
{
    sco[id] = score;
}

The error message corresponds to "sco[ID] = score; "

The type of the expression must be an array type but it resolved to float

I'm confused what I should put in the bracket, the book asks me to put "float[] score" instead of "float[] sco", but it doesn't work, so I edited a bit after several trials. This part of coding generally describes the method of overloading that stores the score for 5 subjects.

And this is my whole coding:

public class Score {
float math, english, physics, chemistry, biology;
float sum, average;
float[] score;
int id;

void setMath(float Math) {
    math = Math;
}

void setEnglish(float English) {
    english = English;
}

void setPhysics(float Physics) {
    physics = Physics;
}

void setChemistry(float Chemistry) {
    chemistry = Chemistry;
}

void setBiology(float Biology) {
    biology = Biology;
}

void setSum(float Sum) {
    sum = math + english + physics + chemistry + biology;
}

void setAverage(float Average) {
    average = sum / 5;
}

float getMath() {
    return math;
}

float getEnglish() {
    return english;
}

float getPhysics() {
    return physics;
}

float getChemistry() {
    return chemistry;
}

float getBiology() {
    return biology;
}

float getSum() {
    return sum;
}

float getAverage() {
    return average;
}

public void setScore(float[] sco)
{
    sco = score;
}

public void setScore(float sco, int id)
{
    sco[id] = score;
}
}

Now my problem solved! Since I just changed like this:

    public void score()
{

}
public void setScore(float[] score)
{
    sco = score;
}

Can anyone tell me why now the problem resolved? Will really appreciate a lot!

回答1:

You are assigning a value of the class variable score to the parameter sco when you should do the opposite. In other words:

Your code says:

sco = score;

But what you should do is:

score = sco;

In both functions you need to switch the order of score and sco so that score gets the value of sco.

As far as your error, in setScore(float sco, int id) you defined parameter sco as a float but you are trying to access it as an array (by saying sco[Id] = score). That is why you are getting your error message.

The type of the expression must be an array type but it resolved to float

Like I said, you can fix this by switching the order again:

sco[Id] = score;

Into:

score[Id] = sco;

EDIT:

As far as this part:

I'm confused what I should put in the bracket, the book asks me to put "float[] score" > instead of "float[] sco", but it doesn't work, so I edited a bit after several trials. This > part of coding generally describes the method of overloading that stores the score for 5 > subjects.

Since you wanted to know how to use the same names for parameters and class variables, as @Smutje mentioned, you should use the keyword this.

That way, there is no ambiguity with which score you are using:

• this.score belongs to your class called Score and can be used in any function inside the class. It is visible to everything inside the class.

• score is a function parameter local to a function setScore() and can only be used inside setScore(). It is only visible inside the function.

Therefore, including everything mentioned, you should make the following changes:

Change:

public void setScore(float sco, int id)
{
    sco[id] = score;
}

void setScore(float[] sco)
{
    sco = score;
}

To:

public void setScore(float score, int id) // changed sco to score
{
    this.score[id] = score;   // switched order, added keyword this
}

void setScore(float[] score) // changed sco to score
{
    this.score = score;  // switched order, added keyword this
}

回答2:

I guess you mixed up the variable names:

void setScore(float[] sco)
{
    sco = score;
}

public void setScore(float sco, int id)
{
    sco[id] = score;
}

because score is the field which you want to populate and sco is the parameter which you want to populate score with. The code above does not change any contents of Score, so try to swap it to

void setScore(float[] sco)
{
    this.score = sco;
}

public void setScore(float sco, int id)
{
    this.score[id] = sco;
}

it also would have helped if you have started using this to mark instance fields explicitly.

回答3:

Check again how you set your score:

void setScore(float[] sco)
{
    sco = score;
}

What is sco? What you want to assign to what?

You are assigning your local variable to the parameter. It should be the other way around. (this.score = sco)