Line 6: copy the value of the variable first into the calculation, its value is 5 Line 4: the value of the variable first is 5 Line 4: copy 5 to the value of the variable first Line 2: the value of the variable second is 23 Line 2: copy 23 to the value of the variable second Line 2: copy the value of the variable first into the calculation, its value is 2 Line 1: the value of the variable first is 2 Line 1: copy the result of the calculation 1 + 1 as the value of the variable first
Let's demonstrate the execution with the following program code:
JAVA MATH CALCULATOR CODE
As you're reading the program, write down the names of any new variables, while making a note of how the values of the variables in the code change line by line. Perhaps the best way to understand a program's execution flow is through the use of pen and paper. 42 = value - fortunately, IDEs provide support on this issue too. The confusion also manifests itself in situations where the programmer accidentally writes e.g.
The third misunderstanding concerns the direction of copying: it's often thought that in executing first = second the value of the variable second is set as the value of the variable first. It only occurs when the program code first = second is executed. This is incorrect assignment - i.e., copying - is a one-off event. Viewing value assignment as creating a dependency instead of being a copy operation: once first = second has been executed, it's often assumed that any change in the value of the variable second is automatically also reflected in the value of the variable first. Hence, the variable second is not modified. This is incorrect, as executing first = second means that the value in the position specified by second is merely copied to the place specified by the variable first. 
Viewing value assignment as a transfer instead of a copy operation: once first = second has been executed, it's often assumed that the value of the variable second has been moved to the value of the variable first, and that the variable second no longer holds a value, or that its value is 0, for instance. Here's three common misunderstandings related to assigning a value to a variable: It's crucial for a programmer to understand that assigning a value to a variable always does the same thing. When a value is assigned to a variable, the same chain of events always occurs: the value on the right-hand side of the equality sign is copied and assigned to the variable on the left-hand side (i.e., copied to the location specified by that variable). When a computer executes program code, it does it one command at a time, always advancing exactly as specified by the code. Loading Misunderstandings Related to the Value of a Variable
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