Converting Strings to Numbers
and Numbers to Strings

Strings to Numbers

Remember: numbers stored in strings must be converted to a numeric type
(such as an int) before they can be used in calculations.

Converting Strings to Numbers:
To convert a string value to a number, the following methods may be used:

  reddot Convert using Integer.parseInt()
The parameter will be converted to a primitive int value. This is the most used method.
The chart below shows notations also for floats and doubles.
Type
Example
int
i = Integer.parseInt(String a);
float
f = Float.parseFloat(String a);
double
d = Double.parseDouble(String a);
computerfix

Example:
String numberString = "1701";
int number = Integer.parseInt(numberString);
System.out.println("The number is " + number + ".");

Output: The number is 1701.

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  reddot Convert using Integer.valueOf()

 

This method will return an Integer object, not a primitive int value.

Example:
String number = "20";
Integer convertedNumber = Integer.valueOf(number);
System.out.println("The number is " + number + ".");

Output: The number is 20.

Trying to convert String number = "twenty"; will cause a runtime error.
The computer has no idea that "twenty" is supposed to be 20.

Trying to convert String number = "10.5"; will also cause an error since it is not an integer.

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beware
The conversions shown here are used to convert Strings (not characters) to numeric values. If you try to use these conversions on a character situation such as numberString.charAt(0) you will not get the desired result. When converting characters to number values, you need to use Character.getNumericValue().

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Numbers to Strings

Converting Numbers to Strings:
To convert a number value to a String, the following methods may be used:

  reddot Convert an integer using Integer.toString()

 

This method is from the Integer class. This method will return a String object representing the int parameter. A popular method.

Example:
int number = 75;
String numberString = Integer.toString(number);

This result is equivalent to String numberString = "75";

The toString method can also be used with the conversion of a double.

String numberString = Double.toString(number);
The converted variable (numberString) will contain the String "75.0".

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  reddot Convert using String.valueOf(int)

 

This method is from the String class. This method will return an Integer object, not a primitive int value.

Example:
int number = 75;
String numberString = String.valueOf(number);

This result is equivalent to String numberString = "75";

This method may be applied to most primitive types.

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