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Every declaration should be for a single variable, on its own line, with an explanatory comment about the role of the variable. Declaring multiple variables in a single declaration can cause confusion regarding the types of the variables and their initial values. If more than one variable is declared in a declaration, care must be taken to ensure that the type and initialized value of the variable is knownself evident.

Noncompliant Code Example

In this noncompliant code example, a programmer or code reviewer might mistakenly believeconceive that the two variables {{src}} and {{c}} are declared as {{int}}. In fact, {{src}} hasis aof type of {{int \[\]}}, while {{c}} has a type of {{int}}.

int src[], c;

Another fallout of this example is that it declares the array in a largely antiquated and unpopular style, with the brackets appearing after the variable name as in type name[]. In practice, arrays are typically declared as type[] name.

Compliant Solution

In this compliant solution, each variable is declared on a separate line. It also uses the preferable style for declaring arrays.

int[] src[];   /* source array */
int c;       /* max value    */

...

In this noncompliant example, a programmer or code reviewer might mistakenly believe that both i and j have been initialized to 1. In fact, only j has been initialized, while i remains uninitialized.

int i, j = 1;

Compliant Solution

In this compliant solution, it is readily apparent that both i and j have been initialized to 1.

int i = 1;
int j = 1;

Nomcompliant Example

In this noncompliant example, the original programmer declared multiple variables, including an array, on the same line. Since even arrays All instances of the type T have access to all Object methods, mistakes of this form may not be immediately detected by the compiler or an IDEmethods of the class Object. However, it is easy to miss that arrays need special treatment when some of these methods are overridden. Oversights of this genre typically go undetected by compilers and IDEs, alike.

public class Example{
  private T a,b,c[],d;

  public Example(T in){
    a = in;
    b = in;
    c = (T[]) new Object[10];
    d = in;
  }

Thus, when it comes time to write something like the toString methoda method of Object like toString() is overridden, a programmer might accidentally write it provide a general implementation for type T without realizing that c is an array. Since the mistake compiles cleanly, it may go undetected.

// The oversight error leads to an incorrect implementation

public String toString(){
  return a.toString() + b.toString() + c.toString() + d.toString();
}

However, the intended toString real intent might have been to invoke toString for each T in () on each individual member of the type T, in array c.

// Correct functional implementation

public String toString(){
  String s = a.toString() + b.toString();
  for(int i = 0; i < c.length; i++){
    s += c[i].toString();
  }
  s += d.toString();
  return s;
}

Compliant Solution

Move To be compliant, move each declaration to a different line, so programmer error of thinking c is a T object, isn't as likely. Furthermore, declare arrays by putting placing the brackets adjacent to the type, as opposed to postfixed to the variable nameusing the postfix notation.

public class Example {
  private T a;
  private T b;
  private T[] c;
  private T d;

  public Example(T in){
    a = in;
    b = in;
    c = (T[]) new Object[10];
    d = in;
  }
}

Exceptions

DCL04-01: Trivial declarations for loop counters, for example, can reasonably be included within a for statement:

for (int i = 0; i < mx; ++i ) {
  /* ... */
}

Risk Assessment

Declaring Failing to declare no more than one variable per declaration can make affect code easier to read and eliminate confusionreadability and cause misinterpretations.

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