A Guide to Java Loops
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1. Overview
In this article, we’ll look at a core aspect of the Java language – executing a statement or a group of statements repeatedly – using loops.
2. Intro to Loops
In programming languages, looping is a feature which facilitates the execution of a set of instructions until the controlling Boolean-expression evaluates to false.
Java provides different types of loops to fit any programming need. Each loop has its own purpose and a suitable use case to serve.
Here are the types of loops that we can find in Java:
3. For Loop
A for loop is a control structure that allows us to repeat certain operations by incrementing and evaluating a loop counter.
For a detailed example, have a look at the dedicated post: Java For Loop.
4. While Loop
The while loop is Java’s most fundamental loop statement. It repeats a statement or a block of statements while its controlling Boolean-expression is true.
For a detailed example, have a look at the dedicated post: Java While Loop.
5. Do-While Loop
The do-while loop works just like the while loop except for the fact that the first condition evaluation happens after the first iteration of the loop.
For a detailed example, have a look at the dedicated post: Java Do-While Loop.
6. Conclusion
In this quick tutorial, we showed the different types of loops that are available in the Java programming language.
We also saw how each loop serves a particular purpose given a suitable use case. We discussed the circumstances that are suitable for a given loop implementation.
As always, examples can be found over on GitHub.
Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.
The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.
Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.
Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes:
Loops in Java
Looping in programming languages is a feature which facilitates the execution of a set of instructions/functions repeatedly while some condition evaluates to true. Java provides three ways for executing the loops. While all the ways provide similar basic functionality, they differ in their syntax and condition checking time.
java provides Three types of Conditional statements this second type is loop statement .
- while loop: A while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as a repeating if statement.
Java
- Flowchart:
- While loop starts with the checking of Boolean condition. If it evaluated to true, then the loop body statements are executed otherwise first statement following the loop is executed. For this reason it is also called Entry control loop
- Once the condition is evaluated to true, the statements in the loop body are executed. Normally the statements contain an update value for the variable being processed for the next iteration.
- When the condition becomes false, the loop terminates which marks the end of its life cycle.
- for loop: for loop provides a concise way of writing the loop structure. Unlike a while loop, a for statement consumes the initialization, condition and increment/decrement in one line thereby providing a shorter, easy to debug structure of looping.
for (initialization condition; testing condition;increment/decrement)
Java
- Flowchart:
- Initialization condition: Here, we initialize the variable in use. It marks the start of a for loop. An already declared variable can be used or a variable can be declared, local to loop only.
- Testing Condition: It is used for testing the exit condition for a loop. It must return a boolean value. It is also an Entry Control Loop as the condition is checked prior to the execution of the loop statements.
- Statement execution: Once the condition is evaluated to true, the statements in the loop body are executed.
- Increment/ Decrement: It is used for updating the variable for next iteration.
- Loop termination:When the condition becomes false, the loop terminates marking the end of its life cycle.
- do while: do while loop is similar to while loop with only difference that it checks for condition after executing the statements, and therefore is an example of Exit Control Loop.
Java
- Flowchart:
- do while loop starts with the execution of the statement(s). There is no checking of any condition for the first time.
- After the execution of the statements, and update of the variable value, the condition is checked for true or false value. If it is evaluated to true, next iteration of loop starts.
- When the condition becomes false, the loop terminates which marks the end of its life cycle.
- It is important to note that the do-while loop will execute its statements atleast once before any condition is checked, and therefore is an example of exit control loop.
Pitfalls of Loops
- Infinite loop: One of the most common mistakes while implementing any sort of looping is that it may not ever exit, that is the loop runs for infinite time. This happens when the condition fails for some reason. Examples:
- Infinite for loop :
Java
infinite while loop:
Java
Java
Another pitfall is that you might be adding something into you collection object through loop and you can run out of memory. If you try and execute the below program, after some time, out of memory exception will be thrown.
Java
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space at java.util.Arrays.copyOf(Unknown Source) at java.util.Arrays.copyOf(Unknown Source) at java.util.ArrayList.grow(Unknown Source) at java.util.ArrayList.ensureCapacityInternal(Unknown Source) at java.util.ArrayList.add(Unknown Source) at article.Integer1.main(Integer1.java:9)
Nested Loop:
Nested loop means a loop statement inside another loop statement.
There are different combinations of loop using for loop, while loop, do-while loop.