How to Use Regex in the String.contains() Method in Java

This article will demonstrate how to utilize regex in Java’s String.contains() function.

The String.contains() function scans for a certain character sequence in a string. If a series of char values are discovered in this string, it returns true; otherwise, it returns false.

Use Regex in the String.contains() Method in Java

It transforms a CharSequence to a String before calling the indexOf function. If indexOf finds the string, it returns 0 or a greater number; otherwise, it returns -1.

So, if a series of char values exists, the contains() function returns true; otherwise, it returns false.

Syntax:

public boolean contains(CharSequence seq) {
  return indexOf(seq.toString()) > -1;
}

Here’s an example of seeing if the charSequence is present or not.

To begin with, create a string type variable named st in the class, and fill it with a string value.

String st = " Hey folks Delft Stack here ";

Now, you can use the .contains() method here:

System.out.println(st.contains("Test"));

class shanii {
  public static void main(String args[]) {
    String st = " Hey folks Delft Stack here ";

    System.out.println(st.contains("Test"));

    System.out.println(st.contains("Delft"));

    System.out.println(st.contains("DS"));

    System.out.println(st.contains("D"));
  }
}

Output:

false
true
false
true

Because it was not contained in the string we named st, the first parameter supplied, "Test", would output false. And since "Delft" was found in the string st, it will return true and vice versa.