Learning Switch Statements in Java

Question

I'm new to Java and am learning switch statements. However, the wrong case (case "two") seems to be matched. I suspect that it's because of the lack of break; after case "one", but can someone please explain to me the logic behind Java switch statements? Why is case "two" matched at all when the values don't even match?

Here is my code:

String a = "one";
switch(a) {
    case "one": System.out.println("a is one");
    case "two": System.out.println("a is two");
    default: System.out.println("numbers");
}

I expected output:

a is one
numbers

But got:

a is one
a is two
numbers

score 3 · Accepted Answer · answered Apr 22 '20 at 04:40

3

The case statement is evaluated from top to bottom, when it finds a match it will enter at that point and continue downwards until a break is found (or it gets to the bottom without finding a match). You cannot drop into "one", skip over "two" and re-enter a default.

Default is used when none of the other cases above it match

answered Apr 22 '20 at 04:40

Jimmy

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`default` isn't expected to be at the bottom (as far as I can remember). – ernest_k Apr 22 '20 at 04:42

score 1 · Answer 2 · answered Apr 22 '20 at 04:39

You need break statements

    String a = "one";
    switch(a) {
        case "one": System.out.println("a is one"); break;
        case "two": System.out.println("a is two"); break;
        default: //
    }
    System.out.println("numbers")

Then maybe print the numbers afterward

score 0 · Answer 3 · answered Apr 22 '20 at 04:57

Each break statement terminates the enclosing switch statement. Control flow continues with the first statement following the switch block. 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.

If all the cases has been checked and not passed then default case will be executed. Thus in your case the code should be like this.

String a = "one";
switch(a) {

    case "one":
        System.out.println("a is one");
        break;

    case "two": 
        System.out.println("a is two");
        break

    default: 
        System.out.println("None of the cases matched ");
}

System.out.println("numbers");

score 0 · Answer 4 · answered Apr 22 '20 at 06:06

In switch statement, the value of the expression is compared with each of the literal values in the case statements. If a match is found l, the code sequence following the case is executed. However, the default statement is optional. The break statement is used inside the switch to terminate a statement sequence. When a break statement is encountered, execution branches to the first of code that follows the entireswitch statement. This has the effect of jumping out of the switch. If you omit the break execution will continue on into the next case.

Learning Switch Statements in Java

4 Answers4