如何删除“Assignment of parameter” is not allowed checkstyle 错误？

Question

I am currently programing a simplified school course system using Java and I'm checking the style using CheckStyle. When I run CheckStyle on one of my classes it gives me two errors that say:

Assignment of parameter 'endTime' is not allowed.
Assignment of parameter 'startTime' is not allowed.

Ive tried multiple things to solve this issue since I can't just create a setter when I'm using that annotation.

I am also using Eclipse btw.

    public void setMeetingDaysAndTime(String meetingDays, int startTime, int endTime) {
    if (meetingDays == null || meetingDays.length() == 0) {
        throw new IllegalArgumentException("Invalid meeting days.");
    }
    if ("A".equals(meetingDays)) {
        this.meetingDays = meetingDays;
        startTime = 0;
        endTime = 0;

This is just a snippet of where my error occurs.

Answer 1

 startTime = 0;

This is re-assigning the parameter startTime .

You didn't paste a lot - if startTime is also a field, this is not assigning the field. Just like the line above it, you'd need this.startTime = 0 , in order to use the field (that this. thing is needed when you shadow the field by taking in an argument that has the same name as the field).

Alternatively, turn this lint checkstyle error off, it's silly. It is attempting to avoid confusion about what that value is during the run of your method, but the fix requires making a new local variable which is itself at least as confusing. In other words, it's a stylecheck that is raising a point where the cure is worse than the disease it is pointing at.

If your intent really is to just carry on with the setMeetingDaysAndTime method as if startTime was 0 , then make a new local variable:

public void setMeetingDaysAndTime(String meetingDays, int startTime_, ...) {
    int startTime = startTime_;

    if ( ... ) {
        startTime = 0;
    }
}

Answer 2

The following description is given for ParameterAssignment :

Disallows assignment of parameters.

Rationale: Parameter assignment is often considered poor programming practice. Forcing developers to declare parameters as final is often onerous. Having a check ensure that parameters are never assigned would give the best of both worlds.

In your case,

startTime = 0;
endTime = 0;

might be an error instead of

this.startTime = 0;
this.endTime = 0;

depending on whether there are the fields startTime and endTime that you actually meant.

To prevent this error (when there is a parameter with the same name as the field), make sure to use this.<fieldName> =...; or use the prefix new for setter method parameters:

public void setMeetingDaysAndTime(String newMeetingDays, int newStartTime, int newEndTime) {
    if (newMeetingDays == null || newMeetingDays.length() == 0) {
        throw new IllegalArgumentException("Invalid meeting days.");
    }
    if ("A".equals(newMeetingDays)) {
        meetingDays = newMeetingDays;
        startTime = 0;
        endTime = 0;

If you really want to assign a new value to the parameter, use a variable with a descriptive name instead.

Example: Instead of re-assigning parameters like:

public void foo(String message, int value) {
    message = message.trim();
    value = value < 0 ? 0 : value;
    bar(message, value);

use local variables instead:

public void foo(String message, int value) {
    String trimmedMessage = message.trim();
    int normalizedValue = value < 0 ? 0 : value;
    bar(trimmedMessage, normalizedValue);

Eclipse provides the ParameterAssignment Checkstyle warning also as compiler warning ( Project > Properties: Java Compiler > Errors/Warnings ): Code style > Parameter assignment . And for the root cause, if this. is missing by mistake, there is the compiler warning Name shadowing and conflicts > Local variable declaration hides another field or variable which is also disabled by default.