Versions Compared

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.
Comment: Broke the NCCE up into 3 seperate NCCEs.

...

Operand 2

Operand 3

Resultant type

type T

type T

type T

boolean

Boolean

boolean

Boolean

boolean

boolean

null

reference

reference

reference

null

reference

byte or Byte

short or Short

short

short or Short

byte or Byte

short

byte, short, char

const int*

byte, short, char if value of int is representable

const int*

byte,short,char

byte, short, char if value of int is representable

Byte

const int*

byte if int is representable as byte

const int*

Byte

byte if int is representable as byte

Short

const int*

short if int is representable as short

const int*

Short

short if int is representable as short

Character

const int*

char if int is representable as char

const int*

Character

char if int is representable as char

other numeric

other numeric

promoted type of the 2nd and 3rd operands

T1 = boxing conversion (S1)

T2 = boxing conversion(S2)

apply capture conversion to lub(T1,T2)

Due to the complicated nature of the rules used to determine the result type of a conditional expression and the potential for unintended type casting, it is recommended that the second and third operands of the conditional expression should always explicitly have the same type.

Noncompliant Code Example

This noncompliant example prints A6565 instead of AAA.

The

...

print statement prints the value of alpha as A, which is of the char type. The third operand '0', is a constant expression of type int whose value can be represented as a char and hence does not cause any numeric promotion.

...

However, this behavior depends on the value of the constant integer expression. Changing the value of the constant integer expression may lead to different behavior, as will be demonstrated in the second noncompliant code example.

Code Block
bgColor#FFCCCC
public class Expr {
  public static void main(String[] args) {
    char alpha = 'A';
    int i = 0;
    System.out.print(true  ? alpha  : 0);
    System.out.print(true  ? alpha  : 12345);
    System.out.print(false ? i : alpha);
  }
}

Compliant Solution

This compliant solution recommends the use of the same types for the second and third operands of the conditional expressions. The clearer semantics help avoid confusion.

Code Block
bgColor#ccccff
public class Expr {
  public static void main(String[] args) {
    char alpha = 'A';
    // Cast 0 as a char i = 0;    to explicitly state that the type of the 
    // conditional expression should be char.
    System.out.print(true  ? alpha  : ((char) 0));
  }
}

Noncompliant Code Example

This noncompliant example prints 65 instead of A.

The print statement prints 65, the integer equivalent of A. This is because of numeric promotion of the second operand alpha to an int, which happens because the third operand, the constant expression '12345', is an int that cannot be represented as a char.

Code Block
bgColor#FFCCCC

public class Expr {
  public static void main(String[] args) {
    char alpha = 'A';declare as char
    System.out.print(true  ? alpha  : 0) 12345);
  }
}

Compliant Solution

The compliant solution casts alpha to int to explicitly state the result type of the conditional expression. Note that while casting 12345 to type char would ensure that both operands in the second nonconforming conditional expression have the same type (and result in A being printed), it would result in data loss when 12345 is converted to a char. Therefore the conforming example casts alpha to int, the wider of the operand types.

Code Block
bgColor#ccccff

public class Expr {
  public static void main(String[] args) {
    char alpha = 'A';
    // Cast alpha as an int to explicitly state that the type of the 
    // conditional expression should be int.
    System.out.print(true  ? ((int) alpha)  : 12345);
  }
}

Noncompliant Code Example

This noncompliant example prints 65 instead of A.

The print statement prints 65. This is because of numeric promotion of the second operand alpha to an int, which happens because the third operand, variable i, is an int.

Code Block
bgColor#FFCCCC

public class Expr {
  public static void main(String[] args) {
    char alpha = 'A';
    int i = 0;
    System.out.print(falsetrue ? ialpha : alphai);
  }
}

...

Compliant Solution

This compliant solution declares i as a char, ensuring that the second and third operands of the conditional expression have the same type.

Code Block
bgColor#ccccff

public class Expr {
  public static void main(String[] args) {
    char alpha = 'A';
    char i = 0;        //declare as char
    System.out.print(true ? alpha : i);
  }
}

Risk Assessment

If the types of the second and third operands in a conditional expression are not the same then the result of the conditional expression may be unexpected.

...