Type Conversions

It is often necessary convert a value from one type to another. For example, we may want to represent an int as a double or a double as a String.

Automatic Type Promotion

When it makes sense, Java automatically converts primitive types. For example, in the following code, 3 is an int literal that is being assigned to x, which is a primitive of type double. Since converting from int to double will not lose information, the conversion is automatic.

double x = 3;

Type Casting Primitives

Consider the following code that attempts to store a double literal in a primitive of type int:

int i = 3.14;

This actually generates a compiler error because such an assignment will result in the loss of information (0.14 cannot be stored in i). If we truly want to do such an assignment, we must make that explicitly clear to the compiler by type casting. In the code below we explicitly cast the 3.14 to an int so that we can then assign it to i.

int i = (int)3.14;

String to Primitive Conversions

If a string contains the value of a primitive, we can convert the string to a primitive representation by using a class method from the appropriate primitive wrapper class. Some examples:

int i = Integer.parseInt("-819");
double x = Double.parseDouble("2.718");
boolean b = Boolean.parseBoolean("true");

Primitive to String Conversions

Converting a primitive value into a String is easily accomplished by concatenating the primitive value to a String. If we just want the primitive value in string form without any additional characters, we can concatenate the primitive to an empty string. Some examples:

String intAsString = "" + 3;
String doubleAsString = "" + 1.618;