Looping string in java

Repeat String N times in Java

In this article, we will learn how to Repeat a given String N times in Java . This is a trick question common in JAVA interviews and the candidate’s evaluation is based on different approaches he/she provides for the problem.

So we will take a deep dive into looking at various ways to solve this problem, starting from the simplest approach to digging deep into how many approaches to ace our concepts. Let us first look at a quick glimpse of Strings in Java.

What is a String in Java?

String in general is a sequence of characters. In Java, String can be represented as an Object and a Literal. Using the String Object we can use the common utility methods provided by the String Class. Let us look at the syntax of declaring a String.

String as a literal or variable :

Note: We can also use the standard utility methods of the String Class with String literals, but the modifications will not reflect in the actual variable. This explains the Immutability of String in Java.

Repeat String N times in Java

Now, without further ado let us outline different ways to solve this problem and explain each method in detail with examples.

Simple For Loop to Repeat String N Times in Java

We can repeat String N times using a for loop in java. This is an iterative way to solve this problem. There are some points to note:

• We take the input string str and a variable string result which will contain the resultant string.
• We will run a loop N times that is given as input.
• On each iteration we will concatenate the result string with the given string like this: result = result + str

In this way, we will have our resultant string repeated N times. Let us understand this with a code snippet.

Using Recursion to Repeat String N Times in Java

Given that we have to repeat a String that involves repeating a process over and over again, we can surmise that Recursion will be helpful to solve this problem. Important points to note:

• If the input String is null or the counter N = 0, we simply return the string.
• Otherwise, we return the input string and concatenate it with the value returned by the recursive call.
• While making each recursive call we decrease the counter N to reach the base condition.

Let us look at the code snippet.

System . out . println ( «The String Repeated » + numberOfTimes + » times using Recursion is : \n» ) ;

String.format() method to Repeat String N Times in Java

The String class in Java has some very useful methods to represent a String in various ways. The format() method of the String class is a method that returns a String in a specific format provided in the arguments. The syntax of the method is :

public static String format(String format, Object. args)

• In the format() method we pass the String as a text to format a number 0 to repeat N times.
• We provide the parameter as ‘0’ to which we convert it to repeat N times.
• Then, we replace the formatted string with the original string.

Let us look at the code implementation.

System . out . println ( «The String Repeated » + numberOfTimes + » times using String.fomrat is : \n» ) ;

Using String.repeat() method in Java 11 to Repeat String N Times

With the introduction of Java 11, a new utility method was added to the String class -> repeat() method. With the repeat() method in the picture, we could repeat any String just by calling the method with the String variable name.

It takes only positive integer values as a parameter and returns a String that is repeated the specified times. The method throws IllegalArgumentException if the count is negative.

public String repeat(int count)

Note: JDK 11.0 or higher must be installed on your machine to use this API.

System . out . println ( «The String Repeated » + numberOfTimes + » times using String.repeat() is : \n» ) ;

Regular Expression – Regex to Repeat String N Times in Java

In Java, with the String replace() method we can define a Regular expression or a regex to modify any String.

• We will create a String using a character or char array of length N, that is the number of times we want the String to repeat.
• Next, we will replace each value in the array with the input String.
• Since the default value of each element in the char array is null we replace ‘\0’ with our input String.

Let us have a look at the code snippet.

System . out . println ( «The String Repeated » + numberOfTimes + » times using String regex is : \n» ) ;

Collections.nCopies() method to Repeat String N Times in Java

With the advent of Java 8, the Collection Framework was introduced in java. Along with this, the Collections class was introduced that provided static methods to operate on the Collection and return the collection.

The nCopies() method of the Collections class generates n number of copies of any object type. It accepts two parameters: n -> the number of copies to make and the object to copy.

T is the generic type. Ex: String, Object, etc.

• The nCopies() method returns an Immutable list of objects. We pass the String to make copies of it.
• After this we join each element in the returned list using the String.join() method.
• We pass «» empty braces as the delimiter to the join() method so the repeats consecutively.

Let us look at the code implementation for this.

System . out . println ( «The String Repeated » + numberOfTimes + » times using Collections is : \n» ) ;

Using Stream API to Repeat String N Times in Java

In Java 8, the introduction of the Stream API and Lambda expressions helped in minimizing the code and add more features of functional programming.

• We use the Stream.generate() method as a Lambda expression and pass the input string as a parameter to generate copies of it. We use the limit() method to limit the number of copies to generate.
• We use the collect() method to collect all the copies of the string.
• To join them use the joining() method of the Collectors class inside the collect() method.

Let us look at the code snippet.

String result = Stream . generate ( ( ) — > str ) . limit ( n ) . collect ( Collectors . joining ( ) ) ;

System . out . println ( «The String Repeated » + numberOfTimes + » times using Stream API is : \n» ) ;

StringUtils Package – Apache Commons Library to Repeat String N Times in Java

The Apache Commons API provides powerful and reusable Java components and dependencies that we can embed into our applications and programs. Here, to repeat a String N times we can use the inbuilt functionality of this package.

We can use the StringUtils class of the Apache Commons Library by importing with the following dependency. For our ease, we will use the JAR file component of the Apache Commons Lang package.

To set up the JAR file component for this package we follow the steps mentioned here.

After this, we can just use the import statement to embed the StringUtils class from the Apache Commons Lang package. The StringUtils class provides the repeat() method as well to repeat a particular input String as we saw in earlier examples.

Let us look at the code for this as well.

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How to loop through a string in java

Solution 3: if you need String array then use this one Solution 1: You can do an enhanced for loop (for java 5 and higher) for iteration on array’s elements: Solution 2: Note that in this case, is 4, so you want to iterate from to get elements , and . but. Assuming that is , you could use (NB: You can do the same thing with arrays) Take a look at The statement and The and statements for more details Solution 2: Use arrays for hora variable.

How to iterate through a String [duplicate]

If you want to use enhanced loop, you can convert the string to charArray

for (char ch : exampleString.toCharArray())

Java String s aren’t character Iterable . You’ll need:

Using Guava (r07) you can do this:

for(char c : Lists.charactersOf(someString))

This has the convenience of using foreach while not copying the string to a new array. Lists.charactersOf returns a view of the string as a List .

Java — Iterate through String with multiple lines, Iterate through String with multiple lines. Ask Question Asked 9 years, 5 months ago. Modified 3 years, 7 months ago. Viewed 26k times 7 I got some data: Note that this is pure Java. Share. Follow edited Jan 22, 2013 at 0:30. answered Jan 22, 2013 at 0:03. supersam654 supersam654.

Loops and Strings in Java

It depends on what you want to achieve and what you hope to gain from it. but.

Assuming that listaH is java.util.List , you could use

(NB: You can do the same thing with arrays)

Take a look at The for statement and The while and do-while statements for more details

Use arrays for hora variable. It can be like

Now you can use any loops, but for is best for your case.

But why waste resource and complexity on new variables? You can do something like listaH.get(4) wherever you need hora5.

 Iterator itr = listaH.iterator(); while(itr.hasNext()) < String element = (String) itr.next(); System.out.print(element + " "); >or for (int i=0;i

if you need String array then use this one

String[] array = listaH.toArray(new String[listaH.size()]); 

How do I loop through an enum in Java?, I want to use a for loop to output all the values in the enum. Something along the lines of this: Something along the lines of this: for(/*each element in the enum*/) < //output the corresponding spanish name >

Iterate through string array in Java

You can do an enhanced for loop (for java 5 and higher) for iteration on array’s elements:

String[] elements = ; for (String s: elements) < //Do your stuff here System.out.println(s); >

String[] elements = < "a", "a", "a", "a" >; for( int i = 0; i

Note that in this case, elements.length is 4, so you want to iterate from [0,2] to get elements 0,1 , 1,2 and 2,3 .

String current = elements[i]; if (i != elements.length - 1)

This makes sure you don’t get an ArrayIndexOutOfBoundsException for the last element (there is no ‘next’ there). The other option is to iterate to i < elements.length - 1 . It depends on your requirements.

Iterate through List in Java, Iterate through List in Java. Lists in java allow us to maintain an ordered collection of objects. Duplicate elements as well as null elements can also be stored in a List in Java. The List interface is a part of java.util package and it inherits the Collection interface. It preserves the order of insertion.

What is the best way to iterate over the lines of a Java String?

BufferedReader bufReader = new BufferedReader(new StringReader(textContent)); 

And use the readLine() method :

String line=null; while( (line=bufReader.readLine()) != null )

To add the Java 8 way to this question:

Arrays.stream(content.split("\\r?\\n")).forEach(line -> /*do something */) 

Of curse you can also use System.lineSeparator() to split if you are sure that the file is comming from the same plattform as the vm runs on.

Or even better use the stream api even more agressiv with filter, map and collect:

String result = Arrays.stream(content.split(System.lineSeparator())) .filter(/* filter for lines you are interested in*/) .map(/*convert string*/) .collect(Collectors.joining(";")); 

I believe you have a better API available starting with Java-11 where you can do the same using the String.lines() API which returns the stream of strings extracted from this string partitioned by line terminators.

Usage of the same could be:-

Stream linesFromString = textContent.lines(); linesFromString.forEach(l -> < //do sth >); 

Important API Note :-

@implNote This method provides better performance than split("\R") by supplying elements lazily and by faster search of new line terminators. 

Loop through JAVA StringTokenizer, No, your code won’t work. While you’re iterating over the tokens you never increment k and l which remain 0 through out; implying that you’re always checking for the first keyword and data type only.. Recommendations. Use the simpler String.split() instead of StringTokenizer which is generally used when …

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How to Iterate over String Array in Java?

To iterate over elements of String Array, use any of the Java Loops like while, for or advanced for loop.

The index of string array starts from 0 to array length – 1. We can use this information and write a loop to iterate over string array elements.

In this tutorial, we will learn how to iterate over string array elements using different looping techniques in Java.

Iterate over String Array using Advanced For Loop

In this example, we will take a string array with four elements and iterate over each of the element using Advanced For Loop in Java.

Java Program

public class Example < public static void main(String[] args)< String strArr[] = ; for(String str: strArr) < System.out.println(str); >> >

Iterate over String Array using For Loop

In this example, we will take a string array with four elements and iterate over each of the element using For Loop in Java.

Java Program

public class Example < public static void main(String[] args)< String strArr[] = ; for(int i = 0; i < strArr.length; i++) < String str = strArr[i]; System.out.println(str); >> >

Iterate over String Array using While Loop

In this example, we will take a string array with four elements and iterate over each of the element using While Loop in Java.

Java Program

public class Example < public static void main(String[] args)< String strArr[] = ; int i = 0; while( i < strArr.length ) < String str = strArr[i]; System.out.println(str); i++; >> >

Conclusion

In this Java Tutorial, we learned how to iterate over elements of String Array in Java, with the help of looping statements.

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