Java面向对象编程(基础部分)
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面向对象编程(基础部分)
类与对象
01：
public class ObjectWorkDemo
{
public static void main(String[] args)
{
Cat cat1 = new Cat();
cat1.name = "Tom";
cat1.age = 3;
cat1.color = "white";
Cat cat2 = new Cat();
cat2.name = "xiaohua";
cat2.age = 100;
cat2.color = "flower";
}
}
class Cat
{
String name;
int age;
String color;
}
对象内存布局
属性/成员变量
注意事项和细节说明
01:
public class PropertiesDetail
{
public static void main(String[] args)
{
Person p1 = new Person();//p1 对象引用 Person() 才是真正的数据空间(真正的对象)
}
}
class Person
{
int age;
String name;
double sal;
boolean isPass;
}
创建对象
创建过程
小练习
成员方法
public class PersonWorkDemo
{
public static void main(String [] args)
{
Person p1 = new Person();
p1.speak();
p1.cal01();
p1.cal02(5);
int res = p1.getSum(10,5);
System.out.println(res);
}
}
class Person
{
String name;
int age;
public void speak()
{
System.out.println("I am good person");
}
public void cal01()
{
int res = 0;
for (int i = 1;i<=1000;i++)
{
res+=i;
}
System.out.println(res);
}
public void cal02(int n)
{
int res = 0;
for (int i = 1;i<=n;i++)
{
res+=i;
}
System.out.println(res);
}
public int getSum(int a,int b)
{
return a+b;
}
}
方法调用机制
成员方法的好处
-
提高代码的复用性
-
可以将实现的细节封装起来，然后供其他用户来调用即可
成员方法的定义
注意事项和使用细节
小练习
01:
public class TestWork
{
public static void main(String [] args)
{
AA a = new AA();
boolean b = a.isOdd(1);
if (b) System.out.println("yes");
else System.out.println("no");
}
}
class AA
{
public boolean isOdd(int num)
{
if num%2!=0?true:false;
}
public void print(int row,int col,char c)
{
for (int i = 0;i<row;i++)
{
for (int j = 0;j<col;j++)
{
System.out.print(c);
}
System.out.println();
}
}
}
成员方法传参机制
- 基本数据类型，传递的是值(值拷贝)，形参的任何改变不影响实参
01:
public class MethodParameter01
{
public static void main(String[] args)
{
int a = 10;
int b = 20;
AA object = new AA();
object.swap(a,b);
System.out.println("a = "+a+" b = "+b);//a = 10 b = 20
}
}
class AA
{
public void swap(int a,int b)
{
System.out.println("a = "+a+" b = "+b);//a = 10 b = 20
int tmp = a;
a = b;
b = tmp;
System.out.println("Later a = "+a+" b = "+b);//a = 20 b = 10
}
}
- 引用类型传递的是地址(传递也是值，但是值是地址)，可以通过形参影响实参
02:
public class MethodParameter02
{
public static void main(String[] args)
{
B b = new B();
int [] arr = {1,2,3};
b.test100(arr);
System.out.println("main:");
for (int i = 0;i<arr.length;i++)
{
System.out.print(arr[i]+"\\t");//200 2 3
}
System.out.println();
Person p = new Person();
p.name = "Tom";
p.age = 10;
b.test200(p);
System.out.println("main age = "+p.age);//1000
}
}
class Person
{
String name;
int age;
}
class B
{
public void test200(Person p)
{
p.age = 1000;
}
public void test100(int [] arr)
{
arr[0] = 200;
for (int i = 0;i<arr.length;i++)
{
System.out.print(arr[i]+"\\t");//200 2 3
}
System.out.println();
}
}
这里的"tom"p会被当做垃圾销毁掉
小练习
public class TestDemo
{
public static void main(String[] args)
{
Person p = new Person();
p.name = "Jack";
p.age = 30;
MyTools myT = new MyTools();
Person p2 = myT.copyPerson(p);
System.out.println(p==p2);//false
}
}
class Person
{
String name;
int age;
}
class MyTools
{
public Person copyPerson (Person p)
{
Person p2 = new Person();
p2.name = p.name;
p2.age = p.age;
return p2;
}
}
如果此时修改p2.name，并不会改变p.name，p2.name会指向一个新地址
方法递归调用
递归举例
01:
public class Recursion01
{
public static void main(String [] args)
{
T t1 = new T();
t1.test(4);
}
}
class T
{
public void test(int n)
{
if (n>2)
{
test(n-1);
}
System.out.println("n = "+n);
}
}
//n = 2
//n = 3
//n = 4
02:
public class Recursion01
{
public static void main(String [] args)
{
T t1 = new T();
t1.test(4);
}
}
class T
{
public void test(int n)
{
if (n>2)
{
test(n-1);
}
else
{
System.out.println("n = "+n);
}
}
}
//n = 2
03:
public class Recursion01
{
public static void main(String [] args)
{
T t1 = new T();
int res = t1.factorial(5);
System.out.println(res);//120
}
}
class T
{
public int factorial(int n)
{
if (n==1)
{
return 1;
}
else
{
return factorial(n-1)*n;
}
}
}
递归重要规则
小练习
01:
class T
{
public int fab(int n)
{
if (n>=1){
if (n==1 || n==2)
{
return 1;
}
else
{
return fab(n-1)+fab(n-2);
}
}
else
{
System.out.println("Input Error");
return -1;
}
}
}
02:
class T
{
public int peach(int day)
{
if (day==10)
{
return 1;
}
else if (day >= 1 && day <= 9)
{
return (peach(day+1)+1)*2;
}
else
{
System.out.println("day在1-10");
return -1;
}
}
}
老鼠出迷宫
03:
略!
汉诺塔
八皇后
略!
方法重载
案例
01:
class MyCalculator
{
public int calculate(int n1,int n2)
{
return n1+n2;
}
public double calculate(int n1,double n2)
{
return n1+n2;
}
public double calculate(double n2,int n1)
{
return n1+n2;
}
public int calculate(double n12019年最新50道java基础部分面试题