Typecast string to int

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Typecast string to int

Frequently, a program ends up with numeric data in a string object--a value entered by the user, for example. The Number subclasses that wrap primitive numeric types ( Byte, Integer, Double, Float, Long, and Short) each provide a class method named valueOf that converts a string to an object of that type. Here is an example, ValueOfDemo , that gets two strings from the command line, converts them to numbers, and performs arithmetic operations on the values: public class ValueOfDemo { public static void main(String[] args) { // this program requires two // arguments on the command line if (args.length == 2) { // convert strings to numbers float a = (Float.valueOf(args[0])).floatValue(); float b = (Float.valueOf(args[1])).floatValue(); // do some arithmetic System.out.println("a + b = " + (a + b)); System.out.println("a - b = " + (a - b)); System.out.println("a * b = " + (a * b)); System.out.println("a / b = " + (a / b)); System.out.println("a % b = " + (a % b)); } else { System.out.println("This program " + "requires two command-line arguments."); } } } The following is the output from the program when you use 4.5 and 87.2 for the command-line arguments: a + b = 91.7 a - b = -82.7 a * b = 392.4 a / b = 0.0516055 a % b = 4.5 Note: Each of the Number subclasses that wrap primitive numeric types also provides a parseXXXX() method (for example, parseFloat()) that can be used to convert strings to primitive numbers. Since a primitive type is returned instead of an object, the parseFloat() method is more direct than the valueOf() method. For example, in the ValueOfDemo program, we could use: float a = Float.parseFloat(args[0]); float b = Float.parseFloat(args[1]); Converting Numbers to Strings Sometimes you need to convert a number to a string because you need to operate on the value in its string form. There are several easy ways to convert a number to a string: int i; // Concatenate "i" with an empty string; conversion is handled for you. String s1 = "" + i; or // The valueOf class method. String s2 = String.valueOf(i); Each of the Number subclasses includes a class method, toString(), that will convert its primitive type to a string. For example: int i; double d; String s3 = Integer.toString(i); String s4 = Double.toString(d); The ToStringDemo example uses the toString method to convert a number to a string. The program then uses some string methods to compute the number of digits before and after the decimal point: public class ToStringDemo { public static void main(String[] args) { double d = 858.48; String s = Double.toString(d); int dot = s.indexOf('.'); System.out.println(dot + " digits " + "before decimal point."); System.out.println( (s.length() - dot - 1) + " digits after decimal point."); } } The output of this program is: 3 digits before decimal point. 2 digits after decimal point. Java String/int FAQ: How do I convert a String to an int data type in Java? Answer: Convert a string to an integer with the parseInt method of the Java Integer class. The parseInt method is to convert the String to an int and throws a NumberFormatException if the string cannot be converted to an int type. Michael Inden (Java Developer) Dr. Daniel Bryant (Big Picture Tech Ltd) Examples Java String to int conversion Overlooking the exception it can throw, use this: int i = Integer.parseInt(myString); If the String signified by the variable myString is a valid integer like "1", "200", and it will be converted to a Java int. If it fails for any reason, the change can throw a NumberFormatException, so the code should be a little longer to account for this. Complete String to int Here is the source code for a whole instance program that demonstrates the Java String to int conversion method, control for a possible NumberFormatException: public class JavaStringToIntExample { public static void main (String[] args) { // String s = "fred"; // use this if you want to test the exception below String s = "100"; try { // the String to int conversion happens here int i = Integer.parseInt(s.trim()); // print out the value after the conversion System.out.println("int i = " + i); } catch (NumberFormatException nfe) { System.out.println("NumberFormatException: " + nfe.getMessage()); } } } Let's discuss As you look into this example, the Integer.parseInt(s.trim()) method is used to change from the string s to the integer i in this line of code: int i = Integer.parseInt(s.trim()); If the change attempt fails ? in case, if you can try to convert the Java String fred to an int -- the Integer parseInt process will throw a NumberFormatException, which you must handle in a try/catch block. In this case, it's not essential to use the String class trim() method but in a real-world program, you must use it, so that's why I've shown it here. Since we're talking about this, here are a few related notes about the String and Integer classes: Integer.toString(int i) is used to convert in the further direction, from an int to a Java String. If you're concerned with converting a String to an Integer object, use the valueOf() method of the Integer class instead of the parseInt() method. If you need to convert strings to additional Java primitive fields, use methods like Long.parseLong(), and so on. In Java, we can use Integer.parseInt() or Integer.valueOf() to convert String to int.Integer.parseInt() ? return primitive int.Integer.valueOf() ? return an Integer object.For position or negative number in String, the convert is the same. String number = "7"; // result = 7 int result = Integer.parseInt(number); // result2 = 7 Integer result2 = Integer.valueOf(number); String number = "-7"; // result = -7 int result = Integer.parseInt(number); // result2 = -7 Integer result2 = Integer.valueOf(number); 1. Integer.java1.1 Review the JDK source code of the Integer class, both method signatures are the same, using parseInt(s,10) to do the conversion, but return a different result. package java.lang; public final class Integer extends Number implements Comparable, Constable, ConstantDesc { public static Integer valueOf(String s) throws NumberFormatException { return Integer.valueOf(parseInt(s, 10)); } public static int parseInt(String s) throws NumberFormatException { return parseInt(s,10); } //... } 2. NumberFormatException2.1 Both Integer.parseInt() and Integer.valueOf(String) methods will throw an NumberFormatException if the input is not a valid digit. String number = "10AA"; Integer result = Integer.parseInt(number); Output java.lang.NumberFormatException: For input string: "10A" at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:68) at java.base/java.lang.Integer.parseInt(Integer.java:658) at java.base/java.lang.Integer.valueOf(Integer.java:989) 3. Integer.parseInt() ? Convert String to int3.1 This example converts a String 999 to a primitive type int. package com.mkyong; public class StringExample1 { public static void main(String[] args) { String number = "999"; try { int result = Integer.parseInt(number); System.out.println(result); } catch (NumberFormatException e) { System.err.println("Unable to convert input string :" + number + " to int"); } } } Output 999 3.2 For String 999AA, an invalid digit, it will throw NumberFormatException, and we catch it and display another more friendly error message. String number = "999AA"; Output Unable to convert input string :999AA to int 4. Integer.valueOf ? Convert String to Integer4.1 This example converts a String 123 to an Integer object. package com.mkyong; public class StringExample2 { public static void main(String[] args) { String number = "123"; try { Integer result = Integer.valueOf(number); System.out.println(result); } catch (NumberFormatException e) { System.err.println("Unable to convert input string :" + number + " to Integer"); } } } Output 123 4.2 For input String number = "123A" Unable to convert input string :123A to Integer 5. Best Practice ? isDigit() + Integer.parseIntThe best practice is to check the inputs; the NumberFormatException thrown is expensive.5.1 Review the following example, we use the regex String.matches("[0-9]*") to check if the inputs are valid digit. package com.mkyong; public class StringExample3 { public static void main(String[] args) { String number = "-100"; if (isDigit(number)) { System.out.println(Integer.parseInt(number)); } else { System.out.println("Please provide a valid digit [0-9]"); } } public static boolean isDigit(String input) { // null or length < 0, return false. if (input == null || input.length() < 0) return false; // empty, return false input = input.trim(); if ("".equals(input)) return false; if (input.startsWith("-")) { // negative number in string, cut the first char return input.substring(1).matches("[0-9]*"); } else { // positive number, good, just check return input.matches("[0-9]*"); } } } Output -100 6. Java 86.1 Developers like Java 8, this example tries to use Java 8 Optional and Stream to convert a String into an Integer. package com.mkyong; import java.util.Optional; public class StringExample4 { public static void main(String[] args) { String number = "10"; Optional result = Optional.ofNullable(number) .filter(StringExample3::isDigit) .map(Integer::parseInt); if (result.isEmpty()) { System.out.println("Please provide a valid digit [0-9]"); } else { System.out.println(result.get()); } } } Output 10 References type cast string to int. typescript cast string to int. type cast string to int python. type cast string to int c++. type cast string to int php. type cast string to int javascript. type cast string to int swift. type cast string to int sql

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