1. 参考 - P123 ~ P126

2. 你将学到

Java中对方法参数能做什么和不能做什么

• 方法不能修改基本数据类型的参数(数值型或布尔型)
• 方法可以改变对象参数的状态
• 方法不能让一个对象参数引用一个新的对象

3. 代码证明

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;}
}