Java學習第二十八天＜訪問修飾符＞＜封裝＞<繼承>
阿新 • • 發佈：2022-03-17
訪問修飾符
package chapter07.D1訪問修飾符.modify1;
public class A {
public int n1=100;
protected int n2=200;
int n3=300;//預設修飾
private int n4=400;
public void m1(){
System.out.println("n1="+n1+"n2="+n2+"n3="+n3+"n4="+n4);
//本類四種類型屬性都能訪問
}
protected void m2(){}
void m3(){}
private void m4(){}
public void hi(){
m1();
m2();
m3();
m4();
//本類四種類型方法都能訪問
}
}
package chapter07.D1訪問修飾符.modify1;
public class B {
public void say(){
A a = new A();
//在同一個包下可訪問public protected 和預設，不能訪問private
System.out.println("n1="+a.n1+"n2="+a.n2+"n3="+a.n3);//訪問不到n4
a.m1();
a.m2();
a.m3();//訪問不到m4
}
}
package chapter07.D1訪問修飾符.modify1;
public class Test {
public static void main(String[] args) {
A a = new A();
a.m1();
B b = new B();
b.say();
}
}
package chapter07.D1訪問修飾符.modify2;
import chapter07.D1訪問修飾符.modify1.A;
public class Test {
public static void main(String[] args) {
A a = new A();
System.out.println(a.n1);//跨包只有public能訪
a.m1();//m2不能
}
}
封裝
package chapter07.D2封裝;
import java.util.Random;
public class AccountTest {
public static void main(String[] args) {
Account a = new Account("greger", 18, "nfvgoesjfn");
}
}
class Account{
private String name;
private double exmoney;
private String key;
public String getName() {
return name;
}
public void setName(String name) {
if (name.length()>=2&&name.length()<=4){
this.name = name;
}else
System.out.println("名字長度有誤，預設為zhengtu");
this.name="zhengtu";
}
public double getExmoney() {
return exmoney;
}
public void setExmoney(double exmoney) {
if (exmoney>20){
this.exmoney = exmoney;
}else {
System.out.println("餘額不足20，預設為0");
this.exmoney=0;
}
}
public String getKey() {
return key;
}
public void setKey(String key) {
if (key.length()==6){
this.key = key;
}else {
System.out.println("密碼必須6位，默然為123456");
this.key="123456";
}
}
public void info(){
System.out.println("name="+this.name+"extrmoney="+this.exmoney+"key="+this.key);
}
public Account(String name, double exmoney, String key) {
setName(name);
setExmoney(exmoney);
setKey(key);
info();
}
}
package chapter07.D2封裝;
import java.util.Random;
public class Encapsulation01 {
public static void main(String[] args) {
/* Person p = new Person();
p.setAge(999);
p.setName("efrefowif");
p.setSalary(66);
p.setJob("帶電");
p.info();*/
//使用構造器
Person p = new Person(999, 66, "joijoij", "帶電");
}
}
class Person{
private int age;
private double salary;
private String name;
private String job;
//快捷鍵 alt+insert
public int getAge() {
return age;
}
public void setAge(int age) {
if (age>1&&age<120){
this.age = age;
}else {
System.out.println("輸入有誤");
Random r = new Random();
this.age= r.nextInt(60);
}
}
public double getSalary() {
//可加許可權
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public String getName() {
return name;
}
public void setName(String name) {
if (name.length()>=2&&name.length()<=6){
this.name = name;
}else {
System.out.println("名字過短或過長");
this.name= "zhengtu";
}
}
public String getJob() {
return job;
}
public void setJob(String job) {
this.job = job;
}
public void info(){
System.out.println("neme:"+this.name+"age:"+this.age+"job:"+this.job+"salary:"+this.salary);
}
public Person(int age, double salary, String name, String job) {
setJob(job);
setSalary(salary);
setAge(age);
setName(name);
info();
}
}
繼承
package chapter07.D3繼承;
//父類
public class Base {
public int n1=100;
protected int n2=200;
int n3=300;
private int n4=400;
public Base(){
System.out.println("Base()父類無參構造器執行....");
}
//若是有參構造器覆蓋了無參構造器
public void test100(){
System.out.println("test100");
}
protected void test200(){
System.out.println("test200");
}
void test300(){
System.out.println("test300");
}
private void test400(){
System.out.println("test400");
}
//私有屬性要想被訪問，提供一個public方法
public int getN4(){
return n4;
}
public void calltest400(){
test400();
}
}
package chapter07.D3繼承;
//子類只能繼承一個父類
public class Sub extends Base{
public Sub() {
//隱藏 super(); 預設呼叫父類無參構造器，super和this必須在構造器第一行，兩者不共存
System.out.println("Sub()子類無參構造器執行....");
//若父類是有參構造器，要有super(引數);
}
public Sub(String dd){
//同理預設呼叫父類無參構造器super();
System.out.println("Sub(String dd)子類有參構造器執行....");
}
public void sayOk(){
System.out.println(n1+""+n2+""+n3+""+getN4());//父類非私有屬性和方法可在子類直接訪問，n4私有不行
test100();
test200();
test300();//私有方法不能用
calltest400();
}
}
package chapter07.D3繼承;
public class ExtendsDetails {
public static void main(String[] args) {
Sub sub = new Sub();
sub.sayOk();
Sub sub2 = new Sub("jack");
}
}
package chapter07.D3繼承;
public class ExtendsEexercise01 {
public static void main(String[] args) {
B b = new B();
}
}
class A{
A(){
System.out.println("a");
}
A(String name){
System.out.println("a name");
}
}
class B extends A{
B(){
this("abc");
System.out.println("b");
}
//預設super();
B(String name){
System.out.println("b name");
}
}
package chapter07.D3繼承;
public class ExtendsExercise02 {
public static void main(String[] args) {
C c = new C();
}
}
class A2{
public A2(){
System.out.println("我是A類");
}
}
class B2 extends A2{
public B2(){
System.out.println("我是B類的無參構造");
}
public B2(String name){
System.out.println(name+"我是B類的有參構造");
}//注意預設
}
class C extends B2{
public C(){
this("hello");//本類構造器
System.out.println("我是C類的無參構造");
}
public C(String name){
super("hahah");
System.out.println("我是c類的有參構造");
}
}
package chapter07.D3繼承;
import javax.jws.soap.SOAPMessageHandlers;
public class Computer {
private String cpu;
private int memory;
private int disk;
public Computer(String cpu, int memory, int disk) {
this.cpu = cpu;
this.memory = memory;
this.disk = disk;
}
public String getDetails(){
return "cpu="+cpu+"memory="+memory+"disk"+disk;}
public String getCpu() {
return cpu;
}
public void setCpu(String cpu) {
this.cpu = cpu;
}
public int getMemory() {
return memory;
}
public void setMemory(int memory) {
this.memory = memory;
}
public int getDisk() {
return disk;
}
public void setDisk(int disk) {
this.disk = disk;
}
}
package chapter07.D3繼承;
public class PC extends Computer{//父類沒有無參構造器會報錯
private String brand;
//繼承設計基本思想：父類構造器完成父類屬性初始化，子類構造器完成子類初始化
public PC(String cpu, int memory, int disk, String brand) {//自動呼叫構造器
super(cpu, memory, disk);//自動呼叫父類有參
this.brand = brand;
}
public String getBrand(){
return brand;
}
public void setBrand(String brand){
this.brand=brand;
}
public void printInfo(){
System.out.println("PC資訊=");
// System.out.println(getCpu()+getMemory()+getDisk());
//呼叫父類getDetails方法，得到相關屬性
System.out.println(getDetails()+"brand="+brand);
}
}
package chapter07.D3繼承;
public class ExtendsExercise03 {
public static void main(String[] args) {
PC pc = new PC("intel", 16, 500, "IBM");
pc.printInfo();
}
}
package chapter07.D3繼承;
public class ExtendsTheory {
public static void main(String[] args) {
Son son = new Son();//記憶體的佈局
System.out.println(son.name);//優先從子類開始訪問，再向上訪問,遇到私有的停止
System.out.println(son.age);
System.out.println(son.hobby);
}
}
class GrandPa{
String name="大頭爺爺";
String hobby="旅遊";
}
class Father extends GrandPa {
String name="大頭爸爸";
int age =39;
}
class Son extends Father{
String name="大頭兒子";
}