Convert String To int – Java

Here’s an example of converting a String to an int primitive using Integer.parseInt()

	String number = "100";
	int integer = Integer.parseInt(number);	

Here’s a unit test for converting a String to an int in java

	@Test
	public void convertStringToInt() {
		String number = "100";
		int integer = Integer.parseInt(number);
		System.out.println(integer);
		assertTrue("Confirm number is the string converted to int", Integer.parseInt(number) == 100);
	}

Output

100

Heres an example of converting a String to an Integer object using Integer.valueOf()

	String number = "10";
	Integer result = Integer.valueOf(number);

Here’s a unit test for converting a String to an Integer object in java

	@Test
	public void convertStringToInteger() {
		String number = "100";
		Integer integer = Integer.valueOf(number);
		System.out.println(integer);
		assertTrue("Confirm number is the string coverted to Integer", Integer.valueOf(number) == 100);
		assertThat("Confirm number is the string coverted to Integer", Integer.valueOf(number),
				is(instanceOf(Integer.class)));
	}

Output

100

Exceptions

NumberFormatException

Both Integer.parseInt() and Integer.valueOf(number) will throw a NumberFormatException if the String isnt in the correct format for conversion to a number

Here’s a junit test as an example

	@Test
	public void convertInvalidStringToInt() {
		String number = "100A";
		int integer = Integer.parseInt(number);
		System.out.println(integer);
		assertTrue("Confirm number is the string coverted to int", Integer.parseInt(number) == 100);
	}

And heres the stacktrace with the NumberFormatException

java.lang.NumberFormatException: For input string: "100A"
     at java.lang.NumberFormatException.forInputString(Unknown Source)
     at java.lang.Integer.parseInt(Unknown Source)
     at java.lang.Integer.parseInt(Unknown Source)

References

The Integer class provides methods for converting an int to a String and a String to an int, and other methods for dealing with int

1. Integer
2. Integer.parseInt() JavaDoc
3. Integer.valueOf() JavaDoc
4. NumberFormatException JavaDoc