1. Reference-P123 ~ P126
2. You will learn
What can and cannot be done with method parameters in Java
- The method cannot modify the parameters of basic data types (numeric or boolean)
- Methods can change the state of object parameters
- Method cannot let an object parameter refer to a new object
3. Code Proof
public class ParamTest {
public static void main(String[] args) {
/**
* Test 1: Methods can`t modify numeric parameters
*/
System.out.println("Testing tripleValue: ");
double percent = 10;
System.out.println("Before: percent=" + percent);
tripleValue(percent);
System.out.println("After: percent=" + percent);
/**
* Test2: Methods can change the state of object parameters
*/
System.out.println("\nTesting tripleSalary: ");
Employee harry = new Employee("Harry", 5000);
System.out.println("Before: salary=" + harry.getSalary());
tripleSalary(harry);
System.out.println("After: salary=" + harry.getSalary());
/**
* Test3: Methods can`t attach new objects to object parameters
*/
System.out.println("\nTesting swap:");
Employee a = new Employee("Alice", 70000);
Employee b = new Employee("Bob", 60000);
System.out.println("Before: a=" + a.getName());
System.out.println("Before: b=" + b.getName());
swap(a, b);
System.out.println("After: a=" + a.getName());
System.out.println("After: b=" + b.getName());
}
public static void tripleValue(double x) {
x = 3 * x;
System.out.println("End of method: x=" + x);
}
public static void tripleSalary(Employee x) {
x.raiseSalary(200);
System.out.println("End of method: salary=" + x.getSalary());
}
public static void swap(Employee x, Employee y) {
Employee temp = x;
x = y;
y = temp;
System.out.println("End of method: x=" + x.getName());
System.out.println("End of method: y=" + y.getName());
}
}
class Employee {
private String name;
private double salary;
public Employee(String n, double s) {
name = n;
salary = s;
}
public String getName() {
return name;
}
public double getSalary() {
return salary;
}
public void raiseSalary(double byPercent) {
double raise = salary * byPercent / 100;
salary += raise;
}
}
