Variable Context and Scope

Assume we are coding at "//CODING HERE".

Our variable scope is:

Local Variables (newWidth and newHeight)
Method Parameters (f1)
Instance Variables (width and height)

Our scope does not include variables in other methods (like reduceBy, newWidth, newHeight).

public class Rectangle {

private int width;
private int height;

public reduce(int reduceBy) {
	int newWidth;
	int newHeight;
}

public void applyFactor(int f1) {
	int newWidth;
	int newHeight;
	//CODING HERE"
}

Declare Then Use Local Variables

Local variables in a method must be declared before they are used.

See example here...

Think Inside the Box

We are coding at "//CODING HERE".

Our variable context includes:

The box for the method we are coding in ("applyFactors")
The next outer box for the class "Rectangle"

Our context excludes other methods (like "reduce").

public class Rectangle { private int width; private int height;

public reduce(int reduceBy) { int foo; int moo; }

public void applyFactors(int factor1, int factor2) { int zoo, yoo; //CODING HERE }

Example Problem

We are using four variables.

Two compile okay
But two cause compile errors

Based on the previous step:

Why do the two work?
Why do the two fail?

public class Rectangle { private int width; private int height;

public reduce(int reduceBy) { int foo; int moo; }

public void applyFactors(int factor1, int factor2) { int zoo, yoo; zoo = 10; //okay yoo = 20; //okay foo = 30; //Compile Error moo = 40; //Compile Error }