Iterate Over the Characters of a String in Java
Last Updated : 28 Feb, 2022
Given string str of length N, the task is to traverse the string and print all the characters of the given string.
Illustration:
Input : “GeeksforGeeks” Output : G e e k s f o r G e e k s
Input. : “Coder” Output : C o d e r
Methods:
- Using Naive Approach
- Using String.toCharArray() method
- Using CharacterIterator
- Using StringTokenizer
- Using String.split() method
- Using Guava Library
- Using String.chars() method
- Using Code Points
Method 1: Naive Approach
The simplest approach to solve this problem is to iterate a loop over the range [0, N – 1], where N denotes the length of the string, using the variable i and print the value of str[i].
Example
Java // Java Program to Iterate Over the Characters of a String // Using Naive Approach // Importing classes from respective packages import java.io.*; import java.util.*; // Main class class GFG { // Method 1 // Function to traverse the string and // print the characters of the string static void traverseString(String str) { // Traverse the string for (int i = 0; i < str.length(); i++) { // Print current character System.out.print(str.charAt(i) + " "); } } // Method 2 // Main driver method public static void main(String[] args) { // Custom input string String str = "GeeksforGeeks"; // Calling the Method 1 traverseString(str); } } OutputG e e k s f o r G e e k s
Time Complexity: O(N)
Auxiliary Space: O(1)
Method 2: Using String.toCharArray() method
In this approach, we convert string to a character array using String.toCharArray() method. Then iterate the character array using for loop or for-each loop.
Example
Java // Java Program to Iterate Over the Characters of a String // Using String.toCharArray() method // Importing classes from respective packages import java.io.*; import java.util.*; // Main class class GFG { // Method 1 // To traverse the string and // print the characters of the string static void traverseString(String str) { char[] ch = str.toCharArray(); // Traverse the character array for (int i = 0; i < ch.length; i++) { // Print current character System.out.print(ch[i] + " "); } } // Method 2 // Main driver method public static void main(String[] args) { // Custom input string String str = "GeeksforGeeks"; // Calling the Method 1 traverseString(str); } } OutputG e e k s f o r G e e k s
Time Complexity: O(N)
Auxiliary Space: O(N)
Method 3: Using CharacterIterator
In this approach, we use the CharacterIterator methods current() to get the current character and next() to move forward by one position. StringCharacterIterator provides the implementation of CharacterIterator.
Example
Java // Java Program to Iterate Over the Characters of a String // Using CharacterIterator // Importing required libraries import java.io.*; import java.text.*; // Main class class GFG { // Method 1 // To traverse the string and // print the characters of the string static void traverseString(String str) { CharacterIterator it = new StringCharacterIterator(str); // Iterate and print current character while (it.current() != CharacterIterator.DONE) { System.out.print(it.current() + " "); // Moving onto next element in the object // using next() method it.next(); } } // Method 2 // Main driver method public static void main(String[] args) { // Custom input string String str = "GeeksforGeeks"; // Calling the Method 1 traverseString(str); } } OutputG e e k s f o r G e e k s
Time Complexity: O(N)
Auxiliary Space: O(1)
Method 4: Using StringTokenizer
In this approach, we use StringTokenizer class in Java. It breaks a string into tokens based on the delimiter. Its usage is discouraged.
StringTokenizer(String str, String delim, boolean flag): The first two parameters have same meaning. The flag serves following purpose. If the flag is false, delimiter characters serve to separate tokens. For example, if string is "hello geeks" and delimiter is " ", then tokens are "hello" and "geeks". If the flag is true, delimiter characters are considered to be tokens. For example, if string is "hello geeks" and delimiter is " ", then tokens are "hello", " " and "geeks".
Example
Java // Java Program to Iterate Over the Characters of a String // Using StringTokenizer // Importing required libraries import java.io.*; import java.util.*; // Main class class GFG { // Method 1 // To traverse the string and // print the characters of the string static void traverseString(String str) { // If returnDelims is true, use the string itself as // a delimiter StringTokenizer st = new StringTokenizer(str, str, true); while (st.hasMoreTokens()) { System.out.print(st.nextToken() + " "); } System.out.println(); // If returnDelims is false, use an empty string as // a delimiter st = new StringTokenizer(str, "", false); while (st.hasMoreTokens()) { System.out.print(st.nextToken() + " "); } } // Method 2 // Main driver method public static void main(String[] args) { // Custom input string String str = "GeeksforGeeks"; /// Calling the above Method1 traverseString(str); } } OutputG e e k s f o r G e e k s GeeksforGeeks
Time Complexity: O(N)
Auxiliary Space: O(N)
Method 5: Using String.split() method
In this approach, we use the split() method of the String class. It splits the string into substrings based on the regular expression provided.
Example
Java // Java Program to Iterate Over the Characters of a String // Using String.split() method // Importing required classes from respective packages import java.io.*; import java.util.*; // Main class class GFG { // Method 1 // To traverse the string and // print the characters of the string static void traverseString(String str) { // Split str around matches of empty string "" String[] substrings = str.split(""); for (String ch : substrings) { System.out.print(ch + " "); } } // Method 2 // main driver method public static void main(String[] args) { // Custom input string String str = "GeeksforGeeks"; // Calling the Method1 to // print the characters of the string traverseString(str); } } OutputG e e k s f o r G e e k s
Time Complexity: O(N)
Auxiliary Space: O(N)
Method 6: Using Guava Library
In this approach, we use Lists.charactersOf(str) method which returns a view of an immutable list of characters.
Example
Java // Java Program to Iterate Over the Characters of a String // Using Guava Library // Importing required classes from respective packages import com.google.common.collect.Lists; import java.io.*; // Main class class GFG { // Method 1 // To traverse the string and // print the characters of the string static void traverseString(String str) { // Using enhanced for loop for (Character ch : Lists.charactersOf(str)) { System.out.print(ch + " "); } // A new line is required System.out.println(); // Using listIterator on the List // List<Characters> // iterator() // lambda Lists.charactersOf(str) .listIterator() .forEachRemaining( ch -> System.out.print(ch + " ")); // A new line is required System.out.println(); // Using method reference with listIterator // List<Characters> // iterator() Lists.charactersOf(str) .listIterator() .forEachRemaining(System.out::print); } // Method 2 // Main driver method public static void main(String[] args) { // Custom input string String str = "GeeksforGeeks"; // Calling the Method1 to // print the characters of the string traverseString(str); } } OutputG e e k s f o r G e e k s G e e k s f o r G e e k s GeeksforGeeks
Time Complexity: O(N)
Auxiliary Space: O(N)
Method 7: Using String.chars() method
In this approach, we use the chars() method of the String class. This method does not return the Stream<Character> object due to performance reasons. It returns an IntStream(stream of integers) object which can be converted to a Stream<Character>(stream of characters).
Example
Java // Java Program to Iterate Over the Characters of a String // Using String.chars() method // Importing classes from required packages import com.google.common.collect.Lists; import java.io.*; // main class class GFG { // Method 1 // to traverse the string and // print the characters of the string static void traverseString(String str) { // Display message for better readability System.out.println( "Auto boxing into Stream<Character>"); // Using method reference str.chars() .mapToObj(Character::toChars) .forEach(System.out::print); str.chars().forEach(System.out::print); // A new line is required System.out.println(); // Using lambda expressions by casting int to char str.chars() .mapToObj(i -> Character.valueOf((char)i)) .forEach(System.out::print); // A new line is required System.out.println(); str.chars() .mapToObj(i -> (char)i) .forEach(System.out::print); // A new line is required System.out.println(); str.chars() .mapToObj( i -> new StringBuilder().appendCodePoint(i)) .forEach(System.out::print); // A new line is required System.out.println(); // Display message for better readability System.out.println( "Without boxing into Stream<Character>"); str.chars().forEach( i -> System.out.print(Character.toChars(i))); // A new line is required System.out.println(); str.chars().forEach(i -> System.out.print((char)i)); // A new line is required for // readability in output clearly System.out.println(); str.chars().forEach( i -> System.out.print( new StringBuilder().appendCodePoint(i))); } // Method 2 // main driver method public static void main(String[] args) { // Custom input string String str = "GeeksforGeeks"; // Calling the Method 1 to // print the characters of the string traverseString(str); } } OutputAuto boxing into Stream<Character> GeeksforGeeks7110110110711510211111471101101107115 GeeksforGeeks GeeksforGeeks GeeksforGeeks Without boxing into Stream<Character> GeeksforGeeks GeeksforGeeks GeeksforGeeks
Time Complexity: O(N)
Auxiliary Space: O(N)
Method 8: Using Code Points
In this approach, we use String.codePoints() method which returns a stream of Unicode values.
Example
Java // Java Program to Iterate Over the Characters of a String // Using Code Points // importing classes from respective packages import com.google.common.collect.Lists; import java.io.*; // main class class GFG { // Method 1 // To traverse the string and // print the characters of the string static void traverseString(String str) { // Display message for better readability System.out.println( "Auto boxing into Stream<Character>"); // Using method reference str.codePoints() .mapToObj(Character::toChars) .forEach(System.out::print); str.codePoints().forEach(System.out::print); // New line is required System.out.println(); // Using lambda expressions by casting int to char str.codePoints() .mapToObj(i -> Character.valueOf((char)i)) .forEach(System.out::print); // New line is required System.out.println(); // now using the codepoints() over the string str.codePoints() .mapToObj(i -> (char)i) .forEach(System.out::print); // New line is required System.out.println(); str.codePoints() .mapToObj( i -> new StringBuilder().appendCodePoint(i)) .forEach(System.out::print); System.out.println(); // Display message for readability in output System.out.println( "Without boxing into Stream<Character>"); str.codePoints().forEach( i -> System.out.print(Character.toChars(i))); System.out.println(); str.codePoints().forEach( i -> System.out.print((char)i)); System.out.println(); str.codePoints().forEach( i -> System.out.print( new StringBuilder().appendCodePoint(i))); } // Method 2 // main driver method public static void main(String[] args) { // Custom input string String str = "GeeksforGeeks"; // Calling the Method1 to // print the characters of the string traverseString(str); } } OutputAuto boxing into Stream<Character> GeeksforGeeks7110110110711510211111471101101107115 GeeksforGeeks GeeksforGeeks GeeksforGeeks Without boxing into Stream<Character> GeeksforGeeks GeeksforGeeks GeeksforGeeks
Time Complexity: O(N)
Auxiliary Space: O(N)