CODEWITHSUNDEEP
java
Shashi
Shashi

Reputation: 359

Convert java.lang.String to java.lang.Number

I have a String object and I need to convert to java.lang.Number.

Number num = null;
Object cellContents = ".475";

If I try to cast the cellContents to Number directly, 

num = (Number) cellContents;

it throws an exception:

E[java.lang.ClassCastException: java.lang.String]:  : java.lang.ClassCastException: java.lang.String

I searched but could not get a complete answer as to how I can achieve this. Please help!!!

Upvotes: 2

Views: 42937

Answers (6)

elifekiz
elifekiz

Reputation: 1506

Firstly, you should cast your object to string.

You can try something like the following code:

Number num = null; 
Object cellContents = ".475";
num = cellContents.toString();  
num = (Number) num;

Upvotes: 1

Sachin Verma
Sachin Verma

Reputation: 3802

You can not simply convert a String into Number directly as they are not in same hierarchy.But good news is Java Wrapper API do most of the task for you automatically IE, convert a valid String into Wrapper you want and throws a NumberFormatException if the passed String is not a valid Number or other Wrapper.

You should use.

Integer.parseInt(String) throws NumberFormatException

OR

Double.parseDouble(String) throws NumberFormatException

they both return Number Integer and Double respectively and both ARE-A Number.

Upvotes: 7

Rohit Jain
Rohit Jain

Reputation: 213261

You can't cast a String to a Number, because they are not covariant (they don't fall in the same inheritance hierarchy).

You can convert the String to float or double using Float#parseFloat() and Double#parseDouble() respectively, which is what you would need in most cases.

Using Float#valueOf(String) and Double#valueOf(String) creates instances of wrapper classes.

So, depending upon what you need, you can use any of them. I'll show here the first parseXXX methods:

float strToFloat = Float.parseFloat(".475");
double strToDouble = Double.parseDouble(".475");

However, if you are dealing with monetory value, or some other value, where floating point precision is of concern, then you should use BigDecimal instead:

BigDecimal number = new BigDecimal(".475");

Upvotes: 7

Abhishek Singh
Abhishek Singh

Reputation: 9765

You cannot cast ".475" to Integer. However you can cast it to Float or Double using 

float x = Float.parseFloat(".475");

or

double y  = Double.parseDouble(".475");

You should search more about Wrapper Classes in Java and AutoBoxing in java to get basic clear. Happy Coding :)

Upvotes: 0

Andy Thomas
Andy Thomas

Reputation: 86411

You can't just cast the reference type. You're getting an exception because the String object to which it points is not a Number object.

You can, however, cast the reference to a String, if you know it's a String. You can convert it to a real value with Double.valueOf( String ) or Float.valueOf( String ). Once you get a double, you can use auto-boxing to turn it into a Double, which isa Number.

Object cellContents = ".475";
Number num = null;
if ( cellContents instanceof String ) {
   try {
       double d = Double.valueOf( (String) cellContents );
       num = (Double) d; // Auto-boxing
   }
   catch ( NumberFormatException e ) {
     ...
  }
}
else {
    ...
}

Upvotes: 7

Thilo
Thilo

Reputation: 262524

Try

num = new BigDecimal((String)cellContents);

Upvotes: 1

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