Does a java switch case statement execute multiple cases for negative int values?

Question

I just run over something strange in my java code:

switch (result) {
            case 0:
                result_amount = 500;
            case 1:
                result_amount = 600;
            case -1:
                result_amount = 700;
    } 

result is from primitive type int. For value 1 case 1 and case -1 are executed.

Is this a normal switch case behaviour? If yes: why?

Answer 1

You need to use the break keyword after a case block:

switch (result) {
        case 0:
            result_amount = all_amounts[i];
        break;
        case 1:
            result_amount = all_amounts[i];
        break;
        case -1:
            result_amount = all_amounts[i+1];
} 

The switch statement will make a jump to the correct case tag, then execute all the code that follow, ignoring potential other case tags. You can consider the switch statement just like a goto one.

Answer 2

Fall Through.

quoting from docs

The break statements are necessary because without them, statements in switch blocks fall through: All statements after the matching case label are executed in sequence, regardless of the expression of subsequent case labels, until a break statement is encountered.

You have to add the break after each case.

          case 1:
          result_amount = 600;
          break; 

Answer 3

Remember:

This is a mistake that almost every beginner will make. That's why I like C# more. It doesn't allow "fall-through".

What you did wrong is you fell-through the switch statement. Try using 0 as the value of result. It will go through all the cases. When a switch case finishes execution, the next case gets executed. That's why we need to add a break; statement for each case of the switch statement.

switch (result) {
            case 0:
                result_amount = 500;
                break;
            case 1:
                result_amount = 600;
                break;
            case -1:
                result_amount = 700;
                break;
} 

But sometimes we want fall-through. For example when we want to calculate number of days in a month:

switch (month) {
    case 1:
    case 3:
    case 5:
    case 7:
    case 8:
    case 10:
    case 12:
        days = 31;
        break;
    case 2:
        days = 28;
    case 4:
    case 6:
    //Lots of code...
}