Java -入门方法参数（自学笔记）

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wx5bfa5d7d5183a 2023-04-10 16:19:51 博主文章分类：编程语言 ©著作权

文章标签 java 编程语言类 System 值调用 文章分类 JavaScript 前端开发

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首先回顾一下在程式设计语言中有关将参数传递给方法(函数)的一些专业术语。按值调用（call by value）表示方法接收的是调用者提供的值。而按引用调用（call by reference）表示方法接收的是调用者提供的变量地址。一个方法可以修改传递引用所对应的变量值，而不能修改传递值调用所对应的变量值。

class Employee  //simplified Employee class
{
    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;
    }
}
public class ParamTest {
    public static void main(String[] args)
    {
        /**
         * Test 1: Method can't modify numeric paramters
         */
        System.out.println("Testing tripleValue:");
        double percent = 10;
        System.out.println("Before: percent=" + percent);
        tripleValue(percent);
        System.out.println("After: percent=" + percent);

        /**
         * Test 2:Methods can change the state of object parameters
         */

        System.out.println("\nTesting tripleSalary:");
        Employee harry = new Employee("Harry", 50000);
        System.out.println("Before: salary="+harry.getSalary());
        tripleSalary(harry);
        System.out.println("After: salary="+harry.getSalary());

        /**
         * Test3: Methods can't attach new objects to objects paramters
         */

         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)  //doesn't work
    {
        x = x*3;
        System.out.println("End of method: x="+x);
    }
    public static void tripleSalary(Employee x) //works
    {
        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());
    }
}
/*
程序运行示例：
Testing tripleValue:
Before: percent=10.0
End of method: x=30.0
After: percent=10.0

Testing tripleSalary:
Before: salary=50000.0
End of method: salary=150000.0
After: salary=150000.0

Testing swap:
Before: a=Alice
Before: b=Bob
End of method: x=Bob
End of method: y=Alice
After: a=Alice
After: b=Bob
*
*/

总结：