How to Convert a String to an Int in Java

How do I convert a String to an int in Java?

String myString = "1234";
int foo = Integer.parseInt(myString);

If you look at the Java documentation you'll notice the "catch" is that this function can throw a NumberFormatException, which you can handle:

int foo;
try {
   foo = Integer.parseInt(myString);
}
catch (NumberFormatException e) {
   foo = 0;
}

(This treatment defaults a malformed number to 0, but you can do something else if you like.)

Alternatively, you can use an Ints method from the Guava library, which in combination with Java 8's Optional, makes for a powerful and concise way to convert a string into an int:

import com.google.common.primitives.Ints;

int foo = Optional.ofNullable(myString)
 .map(Ints::tryParse)
 .orElse(0)

Java String to Integer Conversion

use
int month = Integer.parseInt(stringMonth);

how to convert a string to an int in java and and separate the values of the string?

If your string is strictly of the form "a b" where a is in the range a a - z, and b is a number in the range 0 - 9 then do something like

/* s is your string */
int row = s.charAt(0) - 'a' + 1;
int col = s.charAt(2) - '0' + 1;

where I've exploited the ASCII character number values and the fact that 'a' is a byte data type.

Of course, in production, you ought to pre-validate s (check its length, whether or not the second character is a space etc. You could even use a regular expression check via Java's String.matches method). All you'd have to do is check if

s.matches("[a-z] [0-9]")

is true. My method is a throwback to the good old C days.

Manually converting a string to an integer in Java

And what is wrong with this?

int i = Integer.parseInt(str);

EDIT :

If you really need to do the conversion by hand, try this:

public static int myStringToInteger(String str) {
    int answer = 0, factor = 1;
    for (int i = str.length()-1; i >= 0; i--) {
        answer += (str.charAt(i) - '0') * factor;
        factor *= 10;
    }
    return answer;
}

The above will work fine for positive integers, if the number is negative you'll have to do a little checking first, but I'll leave that as an exercise for the reader.

How to convert String to int and call method on it?

Try using Integer.valueOf(age) insted of (int) age

Converting a String with spaces to an Integer in java

Would .trim work? And if so, how would I use that?

Yes, trim() will work, it will remove leading and trailing spaces from String,

int integer = Integer.parseInt(string.trim());

convert string to int in java

try String.replaceAll

    String str = "No. of Days : 365";
    str = str.replaceAll(".*?(\\d+).*", "$1");
    System.out.println(str);

you will get

365

Converting String to Number in Java

Use NumberFormat. Number cannot be instantiated because it is an abstract class.

 Number number = NumberFormat.getInstance().parse(string);

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