Data conversion in Java

Sometimes we need to convert data types from e.g. a number to a string or vice versa. We explain the basics behind it in this tutorial.
Go on reading to get the full explanation of all conversion and casts between types. All code snippets will work in your preferred IDE.

In the tutorial What are data types in Java we have explained the Java data types. But using them will result quickly into the need to convert between them.

That process is called Java Type Casting or Java Type Cast , and we use type cast in Java when we want to convert an object or variable of one type into another.

1. Data type conversion in Java

Changing a value from one data type to another type is known as data type conversion. There are 2 types of conversions:

1. Widening Conversion
2. Narrowing Conversion

1.1. Widening or Automatic Conversion

This is also named a lower to higher precision conversion and therefore done automatically by the compiler for us. Widening or Automatic conversion takes place when two data types are automatically converted. It can occur when

• The two data types are compatible
• When we assign value of a smaller data type to a bigger data type

So a conversion in this direction will work out of the box:

byte ➡ short ➡ int ➡ long ➡ float ➡ double

Here some examples:

class Low2High {
   public static void main(String[] args) {
      int i = 100;
      long l = i;
      float f = l;
      System.out.println("Int value " +i);
      System.out.println("Long value " +l);
      System.out.println("Float value " +f);
   }
}

The output for this example will be :

Int value 100

Long value 100

Float value 100.0

Here is the screenshot from the Eclipse:

1.2. Narrowing or Explicit Conversion

This is also called a higher to lower precision conversion often by developers named as cast or casting.
So a conversion in this direction will need special handling:

double ➡ float ➡ long ➡ int ➡ short ➡ byte

Since this direction is losing information or precision the machine or compiler cannot decide for the human. Here we have to tell the compiler what he needs to do for us.

class High2Low {
   public static void main(String[] args) {
      double d = 100.05;
      long l = (long)d;
      int i = (int)l;
      System.out.println("Double value " +d);
      System.out.println("Long value " +l);
      System.out.println("Int value " +i);
   }
} 

The output for this example will be:

Double value 100.05

Long value 100

Int value 100

Here is the screenshot from the Eclipse:

2. How to convert values to Strings?

In any programming language we have to handle conversion from a human input (string) to a specific value mostly a number or a different specific type.

2.1. Converting Java int to String

Using Integer.toString(int)

Converting int to String is very common in Java, here is the most popular way to do it:

The integer class has a static method that returns a String object representing the specified int parameter. 

Here is how to do it:

public class Int2String {
   public static void main(String[] args) {
      int number = -125;
      String numberAsString = Integer.toString(number);
      System.out.println(numberAsString);
   }
}

We can reduce the above code to

public class Int2String {
   public static void main(String[] args) {
      System.out.println(Integer.toString(-125));
   }
}

There are other ways to do it, but this is the most popular way is:

public class Int2String {
   public static void main(String[] args) {
      int number = -125;
      System.out.println("anything to note" + number);
   }
}

2.2. Converting Java byte to String

Using Byte.toString(byte b) 

This is similar method to integer to string, and it is used when you need to convert byte to String in Java, you can use this method of Byte class.

Here is an example how to do it:

public class Byte2String {
   public static void main(String[] args) {
      byte b = 20;
      System.out.println(Byte.toString(b));
   }
}

The output of this example will be

20

Here is the screenshot from the Eclipse:

2.3. Converting Java short to String

Using Short.toString(short d)

Similar method as using byte to String, when you need to convert short to String in Java, you can use this method.

Here is how to do it;

public class Short2String {
   public static void main(String[] args) {
      short s = 25;
      System.out.println(Short.toString(s));
   }
}

The output of converting to String will be

25

Here is the screenshot from the Eclipse:

The output of converting to String will be

25

2.4. Converting Java long to String

String.valueOf(long l)

This is an overloaded method, it can be used convert long to String. The method is static method of String class.

Here is an example how to use this method:

public class Long2String {
   public static void main(String[] args) {
      long l = 14861584l;
      String s = String.valueOf(l);
      System.out.println(s);
   }
}

The output for this example will be

14861584

Here is the screenshot from the Eclipse:

2.5. Converting Java double to String

String.valueOf(double d) 

This is an overloaded method used for converting double to String. The valueOf() is the static method of String class.

Here is an example:

public class Double2String {
   public static void main(String[] args) {
      double d = 24.5;
      String s = String.valueOf(d);
      System.out.println(s);
   }
}

The output will be

24.5

Here is the screenshot from the Eclipse:

2.6. Converting Java float to String

Float.toString(float f)

This method converts float to String. The toString() is the static method of float class. 

Here is an example of this method:

public class Float2String {
   public static void main(String[] args) {
      float f = 45.7f;
      String s = Float.toString(f);
      System.out.println(s);
   }
}

The output for this example will be

45.7

Here is the screenshot from the Eclipse:

2.7. Converting Java boolean to String

Boolean.toString(boolean b)

This method converts boolean to String. The toString() is the static method of boolean class. 

Here is an example of this method:

public class Boolean2String {
   public static void main(String[] args) {
      boolean b1 = true;
      boolean b2 = false;
      String s1 = Boolean.toString(b1);
      String s2 = Boolean.toString(b2);
      System.out.println(s1);
      System.out.println(s2);
   }
}

The outputs for this example will be

true

false

Here is the screenshot from the Eclipse:

3. Now we have shown conversion to String, now we can show some conversion to Int

3.1. Converting Java Character to Int

We use char to int Java when we want to convert a char value in int, we define a char (for example char c = 'a';) and than convert it into int. There are few ways to convert it but the simplest way is to just take the char value and initialize it, here is an example;

public class Char2Int {
   public static void main(String[] args ) {
      char c = 'a';
      int i = c;
      System.out.println(i);
   }
}

Now the output will be

97

but let's explain how it works, basically every character has its ASCII value, and when we convert it into int, the int will return its ASCII value.

Here is the screenshot from the Eclipse:

Note: if we put in char number (example char = '1';) when we convert it to int the return value will not be 1, the int will return its ASCII value (in this case 49)

3.2. Converting Java Double to Int

We use double to int Java in cases where we need double value converted in int. It is similar to previous conversion, and this type also has multiple ways of conversion, but we will show you the simplest one:

public class Double2Int {
   public static void main(String[] args ) {
      double d = 4.255;
      int i = (int) d;
      System.out.println(i);
   }
}

This will return

4 

As a result, but even if we put really high decimal value (example 4.9999) the int value will return 4, this method will not round the value.

Here is the screenshot from the Eclipse:

3.3. Converting Java long to int

This conversion is similar to previous one, it is used when we want to convert long value to int, so here is an example:

public class Long2Int {
   public static void main(String[] args ) {
      long l = 4245;
      int i = (int) l;
      System.out.println(i);
   }
}

The output will be

4245

We have already explained how to convert char to int, but what about int to char?

Here is the screenshot from the Eclipse:

3.4. Converting Java Int to Char

Converting int to char java is made by typecasting. Similar to char to int, when int returned ASCII value of char, now we will have ASCII value of int, and char will return its value, here is an example:

public class Int2Char {
   public static void main(String[] args ) {
      int i = 38;
      char c = (char) i;
      System.out.println(c);
   }
}

The output will be

&

If we put any other number and convert it, we would get different characters, because of the ASCII code

Here is the screenshot from the Eclipse: