Java: Casting
Because variables in Java are strictly typed, a common task is to want to convert the value in one variable to that of another type. For instance, if we have a String that contains the text of a number, we need to convert it to a numeric variable before we can perform calculations on it. This process of conversion is known as casting.
The following shows you how to cast between the common data types.
// Given these variables
byte b = 1;
short s = 2;
int i = 3;
long l = 4;
float f = 5.0F;
double d = 6.0;
String s1 = "4";
String s2 = "5.3";
char c = '7'; // Single quotes for char
// To integers
int num1 = Integer.parseInt( s1 );
int num2 = Integer.parseInt( s2 ); // RUN TIME ERROR
int num3 = (int)f;
int num4 = (int)d;
int num5 = (int)l;
int num6 = (int)c;
// To long
long l1 = Long.parseLong( s1 );
long l2 = Long.parseLong( s2 ); // RUN TIME ERROR
long l3 = (long)f;
long l4 = (long)d;
long l5 = (long)l;
long l6 = (long)c;
// To float
float fl1 = Float.parseFloat( s1 );
float fl2 = Float.parseFloat( s2 );
float fl3 = (float)i;
float fl4 = (float)l;
float fl5 = (float)d;
float fl6 = (float)c;
// To doubles
double do1 = Double.parseDouble( s1 );
double do2 = Double.parseDouble( s2 );
double do3 = (double)i;
double do4 = (double)l;
double do5 = (double)d;
double do6 = (double)c;
// To strings
String str1 = Integer.toString( i );
String str2 = Float.toString( f );
String str3 = Double.toString( d );
String str4 = Long.toString( l );
String str5 = Character.toString( c );
Questions
- What is printed?
double d = 78.1;
int fg = (int)d;
System.out.println(fg);
- What is printed?
int p = 3;
double d = 10.3;
int j = (int)5.9;
System.out.println(p + p * d – 3 * j);
- The following code stores a 20 in the variable j:
double j = 61/3;. What small change can you make to this single line of code to make it print the “real” answer to the division?