Learn to check if a string contains the specified substring in Java using the String.contains() API.
1. String.contains() API
The String.contains(substring) searches a specified substring in the current string. It returns true if and only if the substring is found in the given string otherwise returns false
.
Please remember that this method searches in a case-sensitive manner.
Assertions.assertTrue("Hello World, Java!".contains("World")); //searches the whole string
Assertions.assertFalse("Hello World, Java!".contains("world")); //case-sensitive
The contains() internally uses indexOf() to check the index of the substring. If the substring is found then the index will always be greater than '0'
.
2. Null is Not Supported
The String.contains() method does not accept ‘null’ argument and throws NullPointerException.
Assertions.assertThrows(NullPointerException.class, () -> {
"Hello World, Java!".contains(null);
});
3. Regex Not Supported
The argument should be a literal string. If a regular expression is passed as an argument, it is still considered a string literal.
In the following program, we check for the empty space in the string using the regex ‘//s‘ but the result is false.
Assertions.assertFalse("Hello World, Java!".contains("\\s"));
Happy Learning !!
References: String Java Doc
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