Conditional structures: Difference between revisions

Line 3,411:

=={{header|Java}}==

===if-then-else===

<syntaxhighlight lang="java">if(s.equals("Hello World"))

<syntaxhighlight lang="java">if (s.equals("Hello World")) {

{

foo();

⚫

} else if (s.equals("Bye World"))

}

⚫

bar(); // braces optional for one-liners

⚫

else if(s.equals("Bye World"))

⚫

else {

⚫

bar();//~~{}'s~~ optional for one-liners

⚫

else

{

deusEx();

}</syntaxhighlight>

Java also supports [[wp:Short-circuit_evaluation|short-circuit evaluation]]. So in a conditional like this:

<syntaxhighlight lang="java">if(obj != null && obj.foo()){

<syntaxhighlight lang="java">if (obj != null && obj.foo()) {

aMethod();

}</syntaxhighlight>

<tt>obj.foo()</tt> will not be executed if <tt>obj != null</tt> returns false. It is possible to have conditionals without short circuit evaluation using the <tt>&</tt> and <tt>|</tt> operators (from [[Bitwise operations]]). So in this conditional:

<syntaxhighlight lang="java">if(obj != null & obj.foo()){

<syntaxhighlight lang="java">if (obj != null & obj.foo()) {

aMethod();

}</syntaxhighlight>

You will get a null pointer exception if obj is null.

You will get a null pointer exception if <tt>obj</tt> is null.

===ternary===

<syntaxhighlight lang="java">s.equals("Hello World") ? foo() : bar();</syntaxhighlight>

The ternary operator is an expression, and is most often used as such:

<syntaxhighlight lang="java">Object newValue = s.equals("Hello World") ? a : b;</syntaxhighlight>

===switch===

This structure will only work if the code being switched on evaluates to an integer or character. There is no switching on ~~Objects~~ or floating-point types in Java (except for <code>String</code>s in Java 7 and higher).

This structure will only work if the code being switched on evaluates to an integer or character. There is no switching on <code>Object</code>s (except for Java 17 and higher), <code>long</code>s, or floating-point types in Java (except for <code>String</code>s and enum types in Java 7 and higher).

<syntaxhighlight lang="java">switch(c) {

<syntaxhighlight lang="java">switch (c) {

case 'a':

foo();

break;

case 'b':

bar();

default:

foobar();

}</syntaxhighlight>

This particular example can show the "fallthrough" behavior of a switch statement. If c is the character b, then bar() and foobar() will both be called. If c is the character a, only foo() will be called because of the break statement at the end of that case.

Also, the switch statement can be easily translated into an ~~if-else~~ if-else statement. The example above is equivalent to:

Also, the switch statement can be easily translated into an if-else statement. The example above is equivalent to:

<syntaxhighlight lang="java">if(c == 'a'){

<syntaxhighlight lang="java">if (c == 'a') {

foo();

}else if(c == 'b'){

} else if (c == 'b') {

bar();

foobar();

}else{

} else {

foobar();

}</syntaxhighlight>

Cases without breaks at the end require duplication of code for all cases underneath them until a break is found (like the else if block shown here).

===switch expressions===

Switch statements can be expressions. They must be exhaustive, and return a value with the <tt>yield</tt> keyword.

<syntaxhighlight lang=“java”>int x = switch (c) {

case 'a':

foo();

yield 1;

case 'b':

bar();

default:

foobar();

yield 0;

}</syntaxhighlight>

There is also a new syntax, available for both statements and expressions, that does not use fallthrough:

<syntaxhighlight lang=“java”>int y = switch (c) {

case '1', '2' -> 1 // multiple cases can be on one line

default -> { // use a block for multiple statements

foobar();

yield 0;

}

}</syntaxhighlight>

=={{header|JavaScript}}==