java基础_b站郭永峰教程课程记录116-130
116 成员变量和局部变量注意事项讲解
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
// 局部变量名称可以和成员变量名称一样，在方法中使用的时候，采用的是就近原则
Duck duck = new Duck();
duck.name = "小黑";
duck.speak();
}
}
class Duck{
String name;
public void speak() {
String name = "小白";
System.out.println("我是一只可爱吖:" + name);
}
}
117 方法的形式参数是类名的时候如何调用讲解
需要传递该类的对象
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
//创建对象
Dog dog = new Dog();
dog.name = "a";
dog.age = 1;
//调用print方法
// print(Dog);//这是一个类，错误调用
print(dog);//dog是一个对象
}
public static void print(Dog dog) {
System.out.println(dog.name + ":" + dog.age);
}
}
class Dog{
String name;
int age;
public void name() {
}
}
118 匿名对象
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
// 匿名对象：没有给新创建的对象存储在一个变量里
GirlFriend gf = new GirlFriend();
gf.name = "oo";
gf.hometown = "日本";
gf.height = 1.68;
gf.say();
// 直接打印对象,结果：lesson118.GirlFriend@6f539caf
System.out.println(gf);
new GirlFriend();//匿名对象
System.out.println(new GirlFriend());
}
}
class GirlFriend{
String name;
String hometown;
double height;
public void say() {
System.out.println("我是" + name + "来自" + hometown);
}
}
119 匿名对象讲解02
120 练习题
121 水池的小学生编程题
public static void main(String[] args) {
// TODO Auto-generated method stub
// A水池有154吨水，B有82吨，两水池每小时都排出2吨水，多少小时后，a水池的吨数是b水池的4倍。
// test1();
int a = 154;
int b = 82;
int hour = 1;
while(true) {
a -= 2;
b -= 2;
if(a == 4*b) {
System.out.println(hour + "小时");
break;
}
hour ++;
}
}
122 猜猜甲乙丙丁谁说谎
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
int i = 100;
while (i<=500) {
// System.out.println(i);
//先求abc
int a = i/100;
int b = i%100/10;
int c = i%10;
//甲
int j = i%8;//j=0代表整除
//乙
int y = i%9;
//丙
int bing = i%7;
//丁
int ding = a + b +c;
// 判断4种情况：分别是每一个人会说谎的情况
if(y == 0 && bing == 0 && ding == 15) {
System.out.println("甲说谎");
}else if (j == 0 && bing == 0 && ding == 15) {
System.out.println("yi说谎");
}else if (j == 0 && y == 0 && ding == 15) {
System.out.println("bing说谎");
}else if (j == 0 && y == 0 && bing == 0) {
System.out.println("ding说谎");
}
i++;
}
}
}
123 private封装讲解
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
//年龄不能赋值负数，也不能赋值为无穷大
// 封装的解决方案步骤：
// 把age属性声明为私有的；提供一个公共的访问方法来实现年龄的赋值
Person p = new Person();
p.name = "nana";
// p.age = 23;
p.setAge(20);
p.speak();
//获取年龄？提供一个get方法
System.out.println("年龄：" + p.getAge());
}
}
class Person{
String name;
private int age;//只能在类内使用，外界不能使用
public int getAge() {
return age;
}
public void setAge(int myAge) {
if(myAge > 0 && myAge <= 150) {
age = myAge;
}else {
System.out.println("年龄只能是1`150哦~");
}
}
public void speak() {
System.out.println("I'm" + name + "," + age);
}
}
124 this关键字讲解
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
// this关键字特点：代表当前对象的引用；应用场景：用来区别成员变量喝局部变量重名
Employee em = new Employee();
em.name = "刘教练";
em.position = "瑜伽";
em.say();
}
}
//this和外面调用的变量指向同一地址，指的是同一对象
class Employee{
String name;//成员变量（全局变量）
String position;
public void say() {
String name = "胡教练";//局部变量
//this.name：表示访问成员变量
System.out.println("我是"+this.name+"从事" + position);
}
}
我是刘教练从事瑜伽
125 构造方法constructor概述讲解
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
Person p = new Person();
// p.name = "小飞";
// p.age = 50;
p.say();
Person p1 = new Person();
p1.say();
Person p2 = new Person("贾", 30);
p2.say();
Person p3 = new Person("马", 45);
p3.say();
}
}
//ctrl+d 删除行
class Person{
String name;
int age;
//声明一个无参（空参）的构造方法
public Person(){
name = "小飞";
age = 50;
}
//声明一个有参的构造方法
public Person(String myName,int myAge) {
name = myName;
age = myAge;
}
public void say() {
System.out.println("我是" + name + "今年" + age);
}
}
126 构造方法的重载讲解
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
// 构造方法的重载：是指方法名相同，与返回值类型无关（构造方法没有返回值），只看参数列表
//第一种方式调用
Person p1 = new Person();
p1.name = "张飞";
p1.age = 40;
p1.gender = "男";
p1.say();
//第二种方法调用person【空参构造】
Person p2 = new Person();
p2.say();
//第三种方法调用person【有参，2个】
Person p3 = new Person("可爱多", 20);
p3.say();
//第三种方法调用person【有参，3个】
Person p4 = new Person("可爱多", 20, "女");
p4.say();
}
}
class Person{
String name;
int age;
String gender;
public Person(String myName,int myAge,String myGender) {
name = myName;
age = myAge;
gender = myGender;
}
public Person(String myName,int myAge) {
name = myName;
age = myAge;
}
public Person() {
name = "吕布";
age = 20;
gender = "男";
}
public void say() {
System.out.println(name + "," + age + "," + gender);
}
}
127 构造方法的注意事项讲解
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
//如果没有给构造方法，系统会默认提供一个构造方法；如果给出了构造方法，系统默认不给提供无参的构造方法，必须自己写一个无参的才可以
GirlFriend gf = new GirlFriend();
gf.say();
GirlFriend gf1 = new GirlFriend("林志玲", "台湾");
gf1.say();
}
}
class GirlFriend{
String name;
String hometown;
public GirlFriend() {
}
public GirlFriend(String myName,String myHometown) {
name = myName;
hometown = myHometown;
}
public void say() {
System.out.println(name + "," + hometown);
}
}
128 正确的set和构造方法的书写讲解
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
//set/get方法，构造方法
Person p1 = new Person();
p1.name = "关公";
p1.setAge(20);
p1.say();
}
}
class Person{
String name;
private int age;
//以后都这么写
public void setAge(int age) {
this.age = age;
}
// public void setAge(int myAge) {
// age = myAge;
// }
public void say() {
// TODO Auto-generated method stub
System.out.println("say");
}
}
129 成员变量（属性）的三种赋值方式
public class Demo01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
//直接给属性赋值，比较少用
Student stu1 = new Student();
stu1.name = "马云";
stu1.age = 40;
stu1.say();
//直接通过set方法给属性赋值【开发中常用，并且成员变量为private】
Student stu2 = new Student();
stu2.setName("马云");
stu2.setAge(40);
stu2.say();
//构造方法，给对象中属性进行初始化。提供一个有参的构造方法就要提供一个无参的构造方法
Student stu3 = new Student("马云", 30);
stu3.say();
}
}
class Student{
String name;
int age;
public Student() {
// TODO Auto-generated method stub
}
//快捷方式：空白右键source-using fields
public Student(String name, int age) {
super();
this.name = name;
this.age = age;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void say() {
// TODO Auto-generated method stub
System.out.println(name + age);
}
}
130
