How to cast string to int java

Java String to Int – How to Convert a String to an Integer

String objects are represented as a string of characters.

If you have worked in Java Swing, it has components such as JTextField and JTextArea which we use to get our input from the GUI. It takes our input as a string.

If we want to make a simple calculator using Swing, we need to figure out how to convert a string to an integer. This leads us to the question – how can we convert a string to an integer?

In Java, we can use Integer.valueOf() and Integer.parseInt() to convert a string to an integer.

1. Use Integer.parseInt() to Convert a String to an Integer

This method returns the string as a primitive type int. If the string does not contain a valid integer then it will throw a NumberFormatException.

So, every time we convert a string to an int, we need to take care of this exception by placing the code inside the try-catch block.

Let’s consider an example of converting a string to an int using Integer.parseInt() :

Let’s try to break this code by inputting an invalid integer:

As you can see in the above code, we have tried to convert 25T to an integer. This is not a valid input. Therefore, it must throw a NumberFormatException.

Here’s the output of the above code:

Next, we will consider how to convert a string to an integer using the Integer.valueOf() method.

2. Use Integer.valueOf() to Convert a String to an Integer

We will place our code inside the try-catch block when using this method. Let us consider an example using the Integer.valueOf() method:

Now, let’s try to break the above code by inputting an invalid integer number:

Similar to the previous example, the above code will throw an exception.

Here’s the output of the above code:

We can also create a method to check if the passed-in string is numeric or not before using the above mentioned methods.

I have created a simple method for checking whether the passed-in string is numeric or not.

The isNumeric() method takes a string as an argument. First it checks if it is null or not. After that we use the matches() method to check if it contains digits 0 to 9 and a period character.

This is a simple way to check numeric values. You can write or search Google for more advanced regular expressions to capture numerics depending on your use case.

It is a best practice to check if the passed-in string is numeric or not before trying to convert it to integer.

how to cast string to integer at runtime

I am using reflection in java.

I am getting to know the type of method parameter I am passing at run time. So I am fetching the parameter value from file into a string variable.

SO now if i get to know that the parameter type as integer and if i pass an object containting the string value I am getting

argument type mismatch java.lang.IllegalArgumentException: argument type mismatch

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Note that casting can happen only if the two objects belong in the same hierarchy. So this is not casting.

If the only types you are using are String and Integer, checking the type and then using Integer.parseInt might be the simplest thing to do.

However if you have more different types, I would suggest checking out the good old JavaBeans framwork: http://download.oracle.com/javase/tutorial/javabeans/index.html

And especially the PropertyEditors http://download.oracle.com/javase/7/docs/api/java/beans/PropertyEditor.html http://download.oracle.com/javase/7/docs/api/java/beans/PropertyEditorManager.html

The PropertyEditors allow you to set the value as text, and then retrieve the value as correct type. Assuming you have implemented and registered the property editors, the steps to get the correct type are similer to this:

. or You can just adapt the same mechanism to your simple needs by implementing your own conversion framework with similar but simpler interfaces.

Java Program to Convert a String to Int

In Java, while operating upon strings, there are times when we need to convert a number represented as a string into an integer type. We usually do this because we can operate with a wide flexible set of operations over strings. The method generally used to convert String to Integer in Java is parseInt() of String class.

Variants of parseInt() Method

There are two variants of this method:

Syntax:

Parameters:

Note: This parameter is only specific to the second variant of the method.

Return Type: Both methods convert the string into its integer equivalent. The only difference being is that of the parameter radix. The first method can be considered as an equivalent of the second method with radix = 10 (Decimal).

Note: If your String has leading zeroes, the parseInt() method will ignore them.

Exception Thrown: NumberFormatException is thrown by this method if any of the following situations occur.

Remember certain key points associated with both the variants:

Let’s take a random code snippet further understand the illustrations better.

Output:

For the above code, the snippet output is 111. So, in the cases where leading zeroes are important(in binary representations) avoid using the parseInt() method.

Illustrations:

How to use parseInt() Method?

Let us take an example straightaway in order to get used so do the working of parseint() method and implementing the above mentioned as follows:

How to Convert String to Int in Java

I think you will agree with me when I say:

Converting String to int in Java is a REALLY one of the most used operations.

I’ll show 10 methods of how to change String to int with descriptions and examples.

How to Convert a String to an Int in Java Methods Overview

NOTE: It’s impossible to cast String object to primitive int or to Integer object. This code won’t compile. You should use methods described here to parse a string to int.

Integer.parseInt(s)

Converts a String value as a signed primitive int.

Integer.parseInt(s, radix)

Parses a string argument as a signed primitive int in the radix specified by the second argument.

Integer.parseInt(s, beginIndex, endIndex, radix)

Turning a CharSequence value into a signed primitive int in the radix specified by the second argument from beginIndex to endIndex.

Note: The method has no protection against CharSequence mutation during parsing.

Integer.parseUnsignedInt(s)

Converts a String value to an unsigned primitive int.

Integer.parseUnsignedInt(s, radix)

Parses a String argument as an unsigned primitive int in the radix specified by the second argument.

Integer.parseUnsignedInt(s, beginIndex, endIndex, radix)

Turning a CharSequence value into an unsigned primitive int in the radix specified by the second argument from beginIndex to endIndex.

Integer.valueOf(s)

Converts a String to an Integer object.

Integer.valueOf(s, radix)

Parses a String as an Integer object in the radix specified by the second argument.

Integer.decode(s)

Decodes a String into an Integer. Accepts decimal, hexadecimal, and octal numbers in the following format:

NumberUtils.toInt(s)

NumberUtils class contains some useful methods to parse strings. To Include it to the project you should add maven dependency:

and import org.apache.commons.lang3.math.NumberUtils to your class.

Implementation with a default value as a second argument would be useful if you’re not sure what’s inside of the input String and you want to provide a fallback value.

If the string is null, the default value is returned.

Convert String To int Java – Examples | Java

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How to Convert String to int in Java – The following article will let you know the complete information about string to int java, in case if you have any doubts do let me know.

We have different ways to convert a String to int in Java

Our own logic equivalent to – Integer.parseInt()

String To Int Java

Integer.parseInt() – How It Works:

Syntax1 – int parseInt(String);

It converts the given String into an integer. Suppose we give a String “234” as argument to the method, then it returns the integer 234. As this is a static method, we can invoke this using its class name.

Example:

Algorithm for converting string to int without built-in method:

Implementation:

Output:

Integer.decode() – How It Works

An empty String or a String that contains non-digits will result in Number Format Exception.

Ex:

“234A”, “34.54”, “smile”, “”, etc.

Syntax2: int parseInt(String,int);

This is similar to normal parseInt(), but it takes an integer as second argument and this argument represents the radix of the content in the input String.

Suppose we want to convert an octal number (which is in String format) into its equivalent decimal integer then the second argument should be 8.

Similarly, if we want a hexa-decimal String to its decimal number then the second argument should be 16.

Eg: Integer.parseInt(“234”,10); will result in 234

Implementation:

Example:

Integer.parseInt(“234”,2); will result in NumberFormatException as allowed digits in binary(2) number system are 0 and 1 only.

Integer.parseInt(“789”,8); will result in NumberFormatException as allowed digits in octal(8) number system are from 0 to 7 only

string to int java – Integer.valueOf()

It can also be used similar to Integer.parseInt() to convert a String to int. This method also has an overloaded method to take an int (radix) as second argument where as the first argument is a String.

Integer.parseInt() returns the result as a basic (primitive) int type where as Integer.valueOf() returns the result an Integer object.

Integer.parseUnsignedInt()

This is also similar to Integer.valueOf() and Integer.parseInt() but it can work on positive values only.

Algorithm:

Syntax: Integer decode(String);

This method converts the given string into an int and returns an Integer object.