I have the following code:
where
What will happen if the first statement is true?Will Java still check the second statement? Because in order the first statement to be true, the HashMap should not contain the given key, so if the second statement is checked, I will get
So in simple words, if we have the following code
partialHits
is a HashMap. What will happen if the first statement is true?Will Java still check the second statement? Because in order the first statement to be true, the HashMap should not contain the given key, so if the second statement is checked, I will get
NullPointerException
.So in simple words, if we have the following code
would Java check
AzimuthAzimuthb
if a
is false in the first case and if a
is true in the second case?1,16822 gold badges1616 silver badges2828 bronze badges
9 Answers
No, it will not be evaluated. And this is very useful. For example, if you need to test whether a String is not null or empty, you can write:
or, the other way around
If we didn't have 'short-circuits' in Java, we'd receive a lot of NullPointerExceptions in the above lines of code.
Andreas_DAndreas_D97.5k1111 gold badges152152 silver badges235235 bronze badges
Java has 5 different boolean compare operators: &, &&, |, ||, ^
& and && are 'and' operators, | and || 'or' operators, ^ is 'xor'
The single ones will check every parameter, regardless of the values, before checking the values of the parameters.The double ones will first check the left parameter and its value and if
true
(||
) or false
(&&
) leave the second one untouched.Sound compilcated? An easy example should make it clear:Given for all examples:
AND:
Both parameters are checked before the evaluation is done and a NullPointerException will be thrown for the second parameter.
The first parameter is checked and it returns
false
, so the second paramter won't be checked, because the result is false
anyway.The same for OR:
Will raise NullPointerException, too.
The first parameter is checked and it returns
true
, so the second paramter won't be checked, because the result is true
anyway.XOR can't be optimized, because it depends on both parameters.
HardcodedHardcoded5,72822 gold badges1717 silver badges2020 bronze badges
No it will not be checked. This behaviour is called short-circuit evaluation and is a feature in many languages including Java.
Peter van der HeijdenPeter van der Heijden8,88911 gold badge3030 silver badges5151 bronze badges
All the answers here are great but, just to illustrate where this comes from, for questions like this it's good to go to the source: the Java Language Specification.
Section 15:23, Conditional-And operator (&&), says:
The && operator is like & (§15.22.2), but evaluates its right-hand operand only if the value of its left-hand operand is true. [..] At run time, the left-hand operand expression is evaluated first [..] if the resulting value is false, the value of the conditional-and expression is false and the right-hand operand expression is not evaluated. If the value of the left-hand operand is true, then the right-hand expression is evaluated [..] the resulting value becomes the value of the conditional-and expression. Thus, && computes the same result as & on boolean operands. It differs only in that the right-hand operand expression is evaluated conditionally rather than always.
And similarly, Section 15:24, Conditional-Or operator (||), says:
The || operator is like | (§15.22.2), but evaluates its right-hand operand only if the value of its left-hand operand is false. [..] At run time, the left-hand operand expression is evaluated first; [..] if the resulting value is true, the value of the conditional-or expression is true and the right-hand operand expression is not evaluated. If the value of the left-hand operand is false, then the right-hand expression is evaluated; [..] the resulting value becomes the value of the conditional-or expression. Thus, || computes the same result as | on boolean or Boolean operands. It differs only in that the right-hand operand expression is evaluated conditionally rather than always.
A little repetitive, maybe, but the best confirmation of exactly how they work. Similarly the conditional operator (?:) only evaluates the appropriate 'half' (left half if the value is true, right half if it's false), allowing the use of expressions like:
without a NullPointerException.
CowanCowan32.8k1010 gold badges5959 silver badges6262 bronze badges
No, if a is true (in a
or
test), b will not be tested, as the result of the test will always be true, whatever is the value of the b expression.Make a simple test:
will not throw a
Romain LinsolasRomain LinsolasNullPointerException
!61.5k4343 gold badges187187 silver badges258258 bronze badges
Short circuit here means that the second condition won't be evaluated.
If ( A && B ) will result in short circuit if A is False.
If ( A && B ) will not result in short Circuit if A is True.
If ( A || B ) will result in short circuit if A is True.
If ( A || B ) will not result in short circuit if A is False.
user3211238user3211238
No it won't, Java will short-circuit and stop evaluating once it knows the result.
abyxabyx45.6k1515 gold badges7979 silver badges112112 bronze badges
Yes, the short-circuit evaluation for boolean expressions is the default behaviour in all the C-like family.
An interesting fact is that Java also uses the
fortranfortran&
and |
as logic operands (they are overloaded, with int
types they are the expected bitwise operations) to evaluate all the terms in the expression, which is also useful when you need the side-effects.53.3k1818 gold badges115115 silver badges161161 bronze badges
This goes back to the basic difference between & and &&, | and ||
BTW you perform the same tasks many times. Not sure if efficiency is an issue. You could remove some of the duplication.
Peter LawreyPeter Lawrey455k5959 gold badges605605 silver badges996996 bronze badges
Not the answer you're looking for? Browse other questions tagged javaif-statement or ask your own question.
In programming languages, loops are used to execute a set of instructions/functions repeatedly when some conditions become true. There are three types of loops in java.
- for loop
- while loop
- do-while loop
Java For Loop vs While Loop vs Do While Loop
Comparison | for loop | while loop | do while loop |
---|---|---|---|
Introduction | The Java for loop is a control flow statement that iterates a part of the programs multiple times. | The Java while loop is a control flow statement that executes a part of the programs repeatedly on the basis of given boolean condition. | The Java do while loop is a control flow statement that executes a part of the programs at least once and the further execution depends upon the given boolean condition. |
When to use | If the number of iteration is fixed, it is recommended to use for loop. | If the number of iteration is not fixed, it is recommended to use while loop. | If the number of iteration is not fixed and you must have to execute the loop at least once, it is recommended to use the do-while loop. |
Syntax | |||
Example | |||
Syntax for infinitive loop |
The Java for loop is used to iterate a part of the program several times. If the number of iteration is fixed, it is recommended to use for loop.
There are three types of for loops in java.
- Simple For Loop
- For-each or Enhanced For Loop
- Labeled For Loop
Java Simple For Loop
A simple for loop is the same as C/C++. We can initialize the variable, check condition and increment/decrement value. It consists of four parts:
- Initialization: It is the initial condition which is executed once when the loop starts. Here, we can initialize the variable, or we can use an already initialized variable. It is an optional condition.
- Condition: It is the second condition which is executed each time to test the condition of the loop. It continues execution until the condition is false. It must return boolean value either true or false. It is an optional condition.
- Statement: The statement of the loop is executed each time until the second condition is false.
- Increment/Decrement: It increments or decrements the variable value. It is an optional condition.
Syntax:
Flowchart:
For Statement Java Example Template
Example:
Test it NowOutput:
Java Nested For Loop
If we have a for loop inside the another loop, it is known as nested for loop. The inner loop executes completely whenever outer loop executes.
Example:
Output:
Pyramid Example 1:
Output:
Pyramid Example 2:
Output:
Java for-each Loop
The for-each loop is used to traverse array or collection in java. It is easier to use than simple for loop because we don't need to increment value and use subscript notation.
It works on elements basis not index. It returns element one by one in the defined variable.
Syntax:
Example:
Test it NowOutput:
Java Labeled For Loop
List Of Java Statements
We can have a name of each Java for loop. To do so, we use label before the for loop. It is useful if we have nested for loop so that we can break/continue specific for loop.
Usually, break and continue keywords breaks/continues the innermost for loop only.
Syntax:
Example:
Output:
If you use break bb;, it will break inner loop only which is the default behavior of any loop.
Output:
Java Infinitive For Loop
If you use two semicolons ;; in the for loop, it will be infinitive for loop.
Syntax:
Example:
Output:
Now, you need to press ctrl+c to exit from the program.
Next TopicJava While Loop
There may be a situation when you need to execute a block of code several number of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.
Programming languages provide various control structures that allow for more complicated execution paths.
A loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most of the programming languages −
Java programming language provides the following types of loop to handle looping requirements. Click the following links to check their detail.
Sip trunk for home. The codecs in the SIP trunk configuration within Asterisk need to be aligned to use one of the above codecs. As a minimum, offer both alaw and ulaw codecs when sending and receiving calls for widest compatibility with fixed line and mobile operators. Alaw should be. Jun 05, 2010 The register directive registers our Asterisk with the trunk-providers SIP-server, with the username ( 7 in our example case) and the password ( password123 ), that we have specified. We have to register to be able to have calls to our telephone number be forwarded to us.
Sr.No. | Loop & Description |
---|---|
1 | while loop Repeats a statement or group of statements while a given condition is true. It tests the condition before executing the loop body. |
2 | for loop Execute a sequence of statements multiple times and abbreviates the code that manages the loop variable. |
3 | do..while loop Like a while statement, except that it tests the condition at the end of the loop body. |
Loop Control Statements
Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed.
Java supports the following control statements. Click the following links to check their detail.
Sr.No. | Control Statement & Description |
---|---|
1 | break statement Terminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch. |
2 | continue statement Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating. |
Enhanced for loop in Java
As of Java 5, the enhanced for loop was introduced. This is mainly used to traverse collection of elements including arrays.
Syntax
Following is the syntax of enhanced for loop −
- Declaration − The newly declared block variable, is of a type compatible with the elements of the array you are accessing. The variable will be available within the for block and its value would be the same as the current array element.
- Expression − This evaluates to the array you need to loop through. The expression can be an array variable or method call that returns an array.
Example
Live DemoThis will produce the following result −
Output
What is Next?
In the following chapter, we will be learning about decision making statements in Java programming.
A forstatement in Java creates loops in which a counter variable is automatically maintained. The for statement lets you set an initial value for the counter variable, the amount to be added to the counter variable on each execution of the loop, and the condition that’s evaluated to determine when the loop should end.
A for statement follows this basic format:
The three expressions in the parentheses following the keyword for control how the for loop works:
- The initialization-expressionis executed before the loop begins. This expression initializes the counter variable. If you haven’t declared the counter variable before the for statement, you can declare it here.
- The test-expressionis evaluated each time the loop is executed to determine whether the loop should keep looping. This expression tests the counter variable to make sure that it’s still less than or equal to the value you want to count to. The loop keeps executing as long as this expression evaluates to true. When the test expression evaluates to false, the loop ends.
- The count-expressionis evaluated each time the loop executes. Its job is to increment the counter variable.
Here’s a simple for loop that displays the numbers 1 to 10 on the console:
Run this code, and you’ll see the following on the console:
If you declare the counter variable in the initialization statement (as in the previous example), the scope of the counter variable is limited to the for statement itself. Thus, you can use the variable in the other expressions that appear within the parentheses and in the body of the loop, but you can’t use it outside the loop,
If you want, you can declare the counter variable outside the for loop. Then, you can use the counter variable after the loop finishes. For example:
You can exit out of the middle of a loop by using abreak statement. You can also use a continue statement to skip an execution of the loop.
In its most basic form, an if statement executes a single statement or a block of statements if a boolean expression evaluates to true. Here’s the syntax:
The boolean expression must be enclosed in parentheses. If you use only a single statement, it must end with a semicolon. However, the statement can also be a statement block enclosed by braces. In that case, each statement within the block needs a semicolon, but the block itself doesn’t.
Here’s an example:
In this example, a variable named commissionRate is initialized to 0.0 and then set to 0.05 if salesTotal is greater than 10000.0.
Here’s an example that uses a block rather than a single statement:
In this example, the two statements within the braces are executed if salesTotal is greater than $10,000. Otherwise, neither statement is executed.
An if statement can include an else clause that executes a statement or block if the boolean expression is not true. Its basic format is
Here’s an example:
In this example, the commission rate is set to 2% if the sales total is less than or equal to $10,000. If the sales total is greater than $10,000, the commission rate is set to 5%.
Here’s an if statement with an else clause that uses a block instead of a single statement:
The statement that goes in the if or else part of an if-else statement can be any kind of Java statement, including another if or if-else statement. This arrangement is nesting,and an if or if-else statement that includes another if or if-else statement is a nested if statement.
The general form of a nested if statement is this:
In this example, expression-1 is the first to be evaluated. If it evaluates to true, expression-2 is evaluated. If that expression is true, statement-1 is executed; otherwise, statement-2 is executed. But if expression-1 is false, expression-3 is evaluated. If expression-3 is true, statement-3 is executed; otherwise, statement-4is executed.
Here’s an example that implements a complicated commission structure based on two variables, named salesClass and salesTotal:
The trick of using nested if statements is knowing how Java pairs else keywords with if statements. The rule is actually very simple: Each else keyword is matched with the most previous if statement that hasn’t already been paired with an else keyword.