check character in string java code example

Example 1: how to check if there is a character in a string java

String.contains()

Example 2: check if a string contains a character java

string.indexOf('a')

Example 3: find a substring in a string java

package hello;

public class SubStringProblem {

  public static void main(String[] args) {

    // 1st example - You can use the indexOf() method to check if
    // a String contains another substring in Java
    // if it does then indexOf() will return the starting index of
    // that substring, otherwise it will return -1

    System.out
        .println("Checking if one String contains another String using indexOf() in Java");
    String input = "Java is the best programming language";
    boolean isPresent = input.indexOf("Java") != -1 ? true : false;

    if (isPresent) {
      System.out.println("input string: " + input);
      System.out.println("search string: " + "Java");
      System.out.println("does String contains substring? " + "YES");
    }

    // indexOf is case-sensitive so if you pass wrong case, you will get wrong
    // result
    System.out.println("Doing search with different case");
    isPresent = input.indexOf("java") != -1 ? true : false;
    System.out.println("isPresent: " + isPresent); // false because indeOf() is
                                                   // case-sensitive

    // 2nd example - You can also use the contains() method to check if
    // a String contains another String in Java or not. This method
    // returns a boolean, true if substring is found on String, or false
    // otherwise.
    // if you need boolean use this method rather than indexOf()
    System.out
        .println("Checking if one String contains another String using contains() in Java");
    input = "C++ is predecessor of Java";
    boolean isFound = input.contains("Java");
    if (isFound) {
      System.out.println("input string: " + input);
      System.out.println("search string: " + "Java");
      System.out.println("does substring is found inside String? " + "YES");
    }

    // contains is also case-sensitive
    System.out.println("Searching with different case");
    isFound = input.contains("java");
    System.out.println("isFound: " + isFound); // false because indeOf() is
                                               // case-sensitive

  }
}

Output
Checking if one String contains another String using indexOf() in Java
input string: Java is the best programming language
search string: Java
does String contain substring? YES
Doing search with different case
isPresent: false
Checking if one String contains another String using contains() in Java
input string: C++ is the predecessor of Java
search string: Java
does substring is found inside String? YES
Searching for different case
isFound: false

Example 4: java string contains char

/*
    This method returns true if the given string contains
    the char n. It is necessary due to the
    obsolescence of some compilers, which requires us
    to write our own contains method.
    */
    public static boolean contains_char (String main, char secondary)
    {
        boolean contains_result = false;
        for (int i = 0 ; i < input.length () ; i++)
        {
            if (input.charAt (i) == secondary)
            {
                contains_result = true;
                break;
            }
        }
        return contains_result;
    }

/*
for two chars:
*/
public static boolean contains_dualchar (String main, String secondary)
    {
        boolean contains_result = false;
        for (int i = 0 ; i < input.length () ; i++)
        {
            if (input.charAt (i) == secondary.charAt (0))
            {
                if (input.charAt (i + 1) == secondary.charAt (1))
                {
                    contains_result = true;
                    break;
                }
            }
        }
        return contains_result;
    }