- What exactly is
a return value:
- Suppose we have the following
assignment statement:
variableName = callSomeMethod( parame1, param2, ... );
- Return value of a
method =
the replacement value
of a method invocation
In other words:
- The assignment statement:
variableName = callSomeMethod( parame1, param2, ... );will result in the following assignment:
variableName = return-value of the method call;
- The assignment statement:
- Suppose we have the following
assignment statement:
- Possible data types that Java methods can return:
- Methods in Java can
only return
one of the following:
- A value
of a built-in
data type
Example:
- int
- double
- boolean
- And so on...
- A reference (address)
to any data type
Example:
- int[ ] (= a reference (address/location) to an integer array)
- double[ ] (= a reference (address/location) to an double array)
- String (= a reference (address/location) to an array of characters )
- A value
of a built-in
data type
- Methods in Java can
only return
one of the following:
- You have seen that Java methods can
return a built-in type
E.g.: double
public class ToolBox // Methods must be contained inside a class { /* ---------------------------------------- A method called "min" that contains the statements to find the smaller of 2 values a and b --------------------------------------- */ public static double min ( double a, double b ) { double m = 0; if ( a < b ) { m = a; // a is the smaller value } else { m = b; // b is the smaller value } return(m); // Return value of the method } }
- How the method is used:
double x; x = ToolBox.min(4.5, 8.9);
When ToolBox.min(4.5, 8.9) returns, the method invocation is replace by the return value.
In other words:
x = ToolBox.min(4.5, 8.9); Becomes: x = 4.5;
- Program example:
- Write a method that:
- Creates a
double typed array
containing the values
2.3, 3.4 and 4.5
- And returns the created array
- Creates a
double typed array
containing the values
2.3, 3.4 and 4.5
Java program that returns an array:
public static double[] returnArray( ) { double[] x; x = new double[3]; // Create an array of 3 elements x[0] = 2.3; x[1] = 3.4; x[2] = 4.5; return( x ); // Return the **reference** (location) of the array }Explanation:
- Notice that the
return type of the
method is
double[ ].
(double[ ] means: a reference (location/address) of an array of double)
- The variable x is
of the type
double[ ] which means
it contains
the reference (location/address)
of a double typed array
- Therefore, the statement return(x) will return the the reference (location/address) of a double typed array
- Write a method that:
- How to invoke the returnArray method:
- Because we return
a reference to an array of
double, we must then
store the return value
in the same type of variable.
- In other words, we must use
this type of variable:
double[] a;
Example:
public static void main(String[] args) { double[] a; // "a" can contain a ref. to an array of double a = returnArray(); // "a" can receive the return value !!! System.out.println("Array AFTER calling returnArray:"); for (int i = 0; i < a.length; i++) System.out.println( a[i] h ); }
- Because we return
a reference to an array of
double, we must then
store the return value
in the same type of variable.
- Example Program:
(Demo above code)
- Prog file: click here
How to run the program:
- Right click on link and
save in a scratch directory
- To compile: javac ArrayReturn1.java
- To run: java ArrayReturn1