break and switch appears to execute all case statements

Question

In the latest stable release of Java and Eclipse (Kempler), entering the following code and executing it, assuming the package and class names exist:

package         


        

Answer 1

The reason why switch works as it does is that this:

switch(p){  
        case (1):
            x--;
        case (2):
            x = 2;
        case (3):
            x = 3;
        default:
            x++;
    }

is really just syntactic sugar for this (basically):

if (p == 1)
    goto .L1;
else if (p == 2)
    goto .L2;
else if (p == 3)
    goto .L3;
else
    goto .L4;

.L1:
    x--;
.L2:
    x = 2;
.L3:
    x = 3;
.L4:
    x++;

Java doesn't have a goto statement, but C does, and that's where it comes from. So if p is 2, it jumps to .L2 and executes all the statements following that label.

Answer 2

When you don't put a break the switch will execute all other cases that are underneath the entry point

So it actually executes

 x = 2;
 x = 3;
 x++;
 print(x);
 System.out.println(x);

Tks to Pshemo here is a link to the specification of the switch statement

Answer 3

If you want to skip all following cases you need to put a break; at last of this case block or all following case blocks are executed, too.

Have a look: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html

Answer 4

If a condition in a case block is true and there is no return or break, all the other case blocks will be executed regardless if the are true or not.

For a rule of thumb always put a break or return at the end of a case block and you will be 90% right.

switch (p) {
    case (1):
        x--;
        break;
    case (2):
        x = 2;
        break;
    case (3):
        x = 3;
        break;
    default:
        x++;
        break;
}