The scope rules of modern programming languages are rooted in rules developed by
ID: 3661541 • Letter: T
Question
The scope rules of modern programming languages are rooted in rules developed by the earliest block structured languages like Algol. Adding object orientation to languages adds one more layer of complexity to this issue. Let's consider Java, a language with which everyone should be familiar, and explore its scope rules. One aspect of the scope rules of any language is when data or methods can have the same name. Give examples in Java to illustrate a case where declaring two local variables with the same name in same method is permitted and one where it is prohibited. Are the rules governing redeclaration of local names the same as those governing redeclaring local names that rename class-level names? One consequence of scope rules in most languages is that forward references (referring to names before they are declared) are prohibited. Are such forward references always prohibited within a single Java class? Are forward references of local names always prohibited within a single method? If not, provide an example that demonstrates your claim.Explanation / Answer
We cannot use two different local variables with same name within a same method, but variables with same name can be used in different scopes, its illustrated below :
Instead of this, if we try to re-use the same name within the same method, then it will give compile time error : "Variable already defined in the scope";
Forward references can be understood clearly with the below illustration :
As you can see, Java allows you to reference a class variable in a class method, even if the declaration of the variable comes after the method. This is an example of a (legal) forward reference, and support for this is built into the Java compiler.
What you cannot do though, is declare a class variable 'a' that depends on another class variable 'b' that has not been declared yet. Dependent class variable declarations must appear in reverse order of their dependency.
On a tangent, Most, if not all IDE's will warn you if your code contains illegal reference errors.