Fix Code Sample
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ProblemIdentify the problems in the code sample below. Fix the errors so that the code works correctly.
public class MyClass
{
private static int numInst = 0;
int a;
double b;
public static MyClass( double b )
{
this.a = 5;
this.b = b;
numInst++;
}
public static double average( int n1, int n2, int b )
{
int total;
total = n1 + n2 + this.b;
return (double)(total / 3);
}
public static int getNumInst()
{
return this.numInst;
}
public static double square( double )
{
return a*a;
}
public static double cube( double a )
{
return a*getA()*getA();
}
public void setNumInst( int newSum )
{
numInst = newSum;
}
public static void setA( int newA )
{
a = newA;
}
public double getA()
{
return this.a;
}
}
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...By Students"I can recall seeing many of the errors here in the code I wrote during my first year in Computer Science and not having a clue
what was causing them. Something like this wiki page would have saved me a lot of time spent debuggin simple errors.
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SolutionThe first problem with this code is the static constructor. Since this needs to access instance variables, the method must be a instance method. public MyClass( double b )
{
this.a = 5;
this.b = b;
numInst++;
}
The next problem is that our average() method is referencing the instance variable b, rather than the int b passed in as a parameter. To solve this, we just need to remove the this. in front of the reference to b. total = n1 + n2 + b; The getNumInst() method has a similar problem, it tries to reference this, which is not allowed in a static method. Since numInst is a static variable, we can solve this as above, simply removing the reference to this. return numInst; The are two problems with our square() method. First, there is no identifier for the parameter passed in. Second, we are referencing an instance variable from a static method. The solution to both problems is to add a as an identifier in the parameter list. public double square( double a ) The problem with cube() is that is calls an instance method from a static method. This is not allowed. Replace the calls to getA() with one call to square(a). return a*square(a); The setNumInst() method is correct as is, we don't have to make any changes to it. Although there is no reference to this, the variable a referenced by setA() is an instance variable and cannot be called from a static method. To fix this, remove the static from the method signature. public void setA( int newA ) The getA() method works correctly and needs no changes. | ||
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