用户自定义类:
这部分并没有太过于困难的部分,借由代码进行复习:
Employee类的定义:
package com.java.EmployeeTest;
import java.time.*;
public class Employee {
private String name;
private double salary;
private LocalDate hireDay;//以上分别是Employee类的实例域
public Employee(String n,double s,int year,int month,int day) {
name=n;
salary=s;
this.hireDay=LocalDate.of(year, month, day);
}
public String getName() {
return name;
}
public double getSalary() {
return salary;
}
public LocalDate getHireDay() {
return hireDay;
}
public void raiseSalary(double byPercent) {
double raise =salary*byPercent/100;
salary += raise;
}//方法,因为实例域为保证安全性都是用private类型,要引用需要用public方法进行调用
}
main函数:
package com.java.EmployeeTest;
import java.time.*;
public class EmployeeTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
Employee[] staff = new Employee[3];
staff[0] = new Employee("Carl Cracker",75000,1987,12,15);
staff[1] = new Employee("Harry Hacker",50000,1989,10,1);
staff[2] = new Employee("Tony Tester",40000,1990,3,15);
for(Employee e:staff)
e.raiseSalary(5);
for(Employee e: staff)
System.out.println("name="+e.getName()+",salary="+e.getSalary()+",hireDay="+e.getHireDay());
}
}
没啥说的,这部分内容完全可以自己学习。
静态语和静态方法(static)
静态域
现给每个对象添加唯一标识码,nextId(静态域),id
class Employee{
private static int nextId=1;
private Int id;
}
每个对象都拥有自己的id,但这个类所有的实例将共享一个nextId,它属于类,若无对象也存在。
静态常量
Math类中定义了一个静态常量:
public class Math{
……
public static final double PI = 3.14159265358979323846;
……
}
在程序中,可以直接调用类来获得常量,即Math.PI
另一个多次使用的静态常态是System.out.。
public class System{
……
public static final PrintStream out =..;
......
}
静态方法
静态方法是一种不能向对象实施操作的方法
例如:Math类的pow方法就是一个静态方法。表达式:Math.pow(x,a);计算x的a次幂;
可以认为静态方法是没有this参数的方法。
附:若对静态域初始化代码比较复杂,可以用:
static{
……
……
……}
这样表示
重点:静态方法中是不能调用非静态域。形参可以和非静态变量一样,但并非表达同一意思。
代码一览:
package com.java.StaticTest;
public class Employee {
private static int nextId=1;
private String name;
private double salary;
private int id;
public Employee (String n, double s) {
name=n;
salary=s;
id=0;
}
public String getName() {
return name;
}
public double getSalary() {
return salary;
}
public int getId()
{
return id;
}
public void setId() {
id=nextId;
nextId++;
}
public static int getNextId() {
return nextId;
}
public static void main(String[] args) {
Employee e =new Employee("Harry",50000);
System.out.println(e.getName()+" "+e.getSalary());
}
}
package com.java.StaticTest;
public class StaticTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
Employee[] staff = new Employee[3];
staff[0]=new Employee("Tom",40000);
staff[1]=new Employee("Dick",60000);
staff[2]=new Employee("Harry",65000);
for (Employee e:staff) {
e.setId();
System.out.println("name="+e.getName()+",id="+e.getId()+",salary="+e.getSalary());
}
int n = Employee.getNextId();
System.out.println("Next available id="+n);
}
方法参数
程序设计语言中参数传递方法有两种
一种是按值调用,一种是按引用调用
按值调用即方法接受的是调用者提供的值,即得到一个所求的值的拷贝值,方法不能修改传递给他们的任何参数变量的内容
按引用调用即方法节后的是调用者提供的变量地址。
java采用的是按值调用。
代码验证:package com.java.ParamTest;
public 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;
}
}
package com.java.ParamTest;
public class ParamTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println("Testing tripleValue:");
double percent=10;
System.out.println("Before :percent="+percent);
tripleValue(percent);
System.out.println("After:percent="+percent);
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());
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 tripleSalary(Employee x) {
// TODO Auto-generated method stub
x.raiseSalary(200);
System.out.println("End of method:salary="+x.getSalary());
}
public static void tripleValue(double x) {
// TODO Auto-generated method stub
x=3*x;
System.out.println("End of method:x="+x);
}
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());
}
}
结果: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
可以分析出,方法参数分为两个类型:
基本数据类型;
对象引用;
其中基本数据类型完成时对原本数据的拷贝,所有操作都是对其拷贝的内容进行操作,与原数据无关。
而对于对象引用是因为副本指向的也是new出来的地址,故会对其改变。
而交换的也是副本,并非本身,在交换完之后,就将其丢弃。故不变。
原文地址:https://www.cnblogs.com/zzuzhouxiang/p/10328302.html