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Convert String to Integer in Groovy
Last modified: June 2, 2022
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1. Overview
In this short tutorial, we'll show different ways to convert from String to Integer in Groovy.
2. Casting with as
The first method that we can use for the conversion is the as keyword, which is the same as calling the class's asType() method:
@Test
void givenString_whenUsingAsInteger_thenConvertToInteger() {
def stringNum = "123"
Integer expectedInteger = 123
Integer integerNum = stringNum as Integer
assertEquals(integerNum, expectedInteger)
}Like the above, we can use as int:
@Test
void givenString_whenUsingAsInt_thenConvertToInt() {
def stringNum = "123"
int expectedInt = 123
int intNum = stringNum as int
assertEquals(intNum, expectedInt)
}3. toInteger
Another method is from the Groovy JDK extension for java.lang.CharSequence:
@Test
void givenString_whenUsingToInteger_thenConvertToInteger() {
def stringNum = "123"
int expectedInt = 123
int intNum = stringNum.toInteger()
assertEquals(intNum, expectedInt)
}4. Integer#parseInt
A third way is to use Java's static method Integer.parseInt():
@Test
void givenString_whenUsingParseInt_thenConvertToInteger() {
def stringNum = "123"
int expectedInt = 123
int intNum = Integer.parseInt(stringNum)
assertEquals(intNum, expectedInt)
}5. Integer#intValue
An alternative method is to create a new Integer object and call its intValue method:
@Test
void givenString_whenUsingIntValue_thenConvertToInteger() {
def stringNum = "123"
int expectedInt = 123
int intNum = new Integer(stringNum).intValue()
assertEquals(intNum, expectedInt)
}Or, in this case, we can also use just new Integer(stringNum):
@Test
void givenString_whenUsingNewInteger_thenConvertToInteger() {
def stringNum = "123"
int expectedInt = 123
int intNum = new Integer(stringNum)
assertEquals(intNum, expectedInt)
}6. Integer#valueOf
Similar to Integer.parseInt(), we can also use Java's static method Integer#valueOf:
@Test
void givenString_whenUsingValueOf_thenConvertToInteger() {
def stringNum = "123"
int expectedInt = 123
int intNum = Integer.valueOf(stringNum)
assertEquals(intNum, expectedInt)
}7. DecimalFormat
And for our last method, we can apply Java's DecimalFormat class:
@Test
void givenString_whenUsingDecimalFormat_thenConvertToInteger() {
def stringNum = "123"
int expectedInt = 123
DecimalFormat decimalFormat = new DecimalFormat("#")
int intNum = decimalFormat.parse(stringNum).intValue()
assertEquals(intNum, expectedInt)
}8. Exception Handling
So, if conversion fails, like if there are non-numeric characters, a NumberFormatException will be thrown. Additionally, in the case where String is null, NullPointerException will be thrown:
@Test(expected = NumberFormatException.class)
void givenInvalidString_whenUsingAs_thenThrowNumberFormatException() {
def invalidString = "123a"
invalidString as Integer
}
@Test(expected = NullPointerException.class)
void givenNullString_whenUsingToInteger_thenThrowNullPointerException() {
def invalidString = null
invalidString.toInteger()
}To prevent this from happening, we can use the isInteger method:
@Test
void givenString_whenUsingIsInteger_thenCheckIfCorrectValue() {
def invalidString = "123a"
def validString = "123"
def invalidNum = invalidString?.isInteger() ? invalidString as Integer : false
def correctNum = validString?.isInteger() ? validString as Integer : false
assertEquals(false, invalidNum)
assertEquals(123, correctNum)
}9. Summary
In this short article, we've shown some effective ways to switch from String to Integer objects in Groovy.
When it comes to choosing the best method to convert an object type, all of the above are equally good. The most important thing is to avoid errors by first checking if the value of the String in our application can be non-numeric, empty, or null.
As usual, all code examples can be found over on GitHub.
