整数四个字节拆分合并
package day0703;
import java.util.Arrays;
import java.util.Scanner;
public class Test1 {
public static void main(String[] args) {
System.out.print("输入整数:");
int i = new Scanner(System.in).nextInt();
IntByte obj = new IntByte(i);
System.out.println(obj.getInt());
System.out.println(Arrays.toString(obj.getBytes()));
IntByte obj2 = new IntByte(obj.getBytes());
System.out.println(obj2.getInt());
}
}
package day0703;
import java.util.Arrays;
public class IntByte {
int n;
byte[] bytes;
public IntByte(byte[] a) {
int r = 0;
r = r | ((a[0]&0x000000FF)<<24);
r = r | ((a[1]&0x000000FF)<<16);
r = r | ((a[2]&0x000000FF)<<8);
r = r | ((a[3]&0x000000FF)<<0);
this.n = r;
this.bytes = a;
}
public IntByte(int n) {
this.n = n;
this.bytes = new byte[4];
int num = 24;
for (int i =0;i<this.bytes.length;i++)
{
this.bytes[i] = (byte)(n>>num);
num-=8;
}
}
public int getInt()
{
return n;
}
public byte[] getBytes()
{
return Arrays.copyOf(bytes,4);
}
}
学生
package day0704;
public class Student {
int id;
String name;
String gender;
int age;
public Student() {
}
public Student(int id, String name, String gender, int age) {
this.id = id;
this.name = name;
this.gender = gender;
this.age = age;
}
public Student(int id, String name, String gender) {
this(id,name,gender,0);
}
public Student(int id, String name) {
this(id,name,null);
}
public String toString()
{
return id+","+name+","+gender+","+age;
}
}
package day0704;
public class Test1 {
public static void main(String[] args) {
Student s1 = new Student();
Student s2 = new Student(3,"张三");
Student s3 = new Student(4,"李四","男");
Student s4 = new Student(5,"王五","女",18);
System.out.println(s1);
System.out.println(s2);
System.out.println(s3);
System.out.println(s4);
}
}
This关键字
This.xxx this特殊引用,引用当前对象的内存地址
This(…):构造方法之间调用
方法重载overload
同名不同参
println()
println(int)
println(double)
println(char)
println(String)
println(…)
继承
代码复用
单继承:一个类只能继承一个父类
构造方法不继承
私有成员不继承
Person
package day0705;
public class Test1 {
public static void main(String[] args) {
Person person = new Person("张三", 22,"男");
Student student = new Student();
Employee employee = new Employee();
student.name = "李四";
student.gender = "女";
student.age = 18;
student.school = "家里蹲大学";
employee.name = "王五";
employee.gender = "女";
employee.age = 17;
employee.salary = 12000;
System.out.println(person.toString());
System.out.println(student.toString());
System.out.println(employee.toString());
}
}
package day0705;
public class Person {
String name;
int age;
String gender;
public Person() {
}
public Person(String name, int age, String gender) {
this.name = name;
this.age = age;
this.gender = gender;
}
public String toString()
{
return name+","+gender+","+age;
}
}
package day0705;
public class Student extends Person {
String school;
}
package day0705;
public class Employee extends Person {
double salary;
}
父类构造方法
先创建父类对象时,也会先执行父类的构造方法
默认执行无参构造方法
package day0705;
public class Test2 {
public static void main(String[] args) {
new Student();
new Student("张三",22,"男","学校");
}
}
package day0705;
public class Student extends Person {
String school;
public Student() {
System.out.println("student无参");
}
public Student(String name, int age, String gender, String school) {
super(name, age, gender);
this.school = school;
System.out.println("shcool全参");
}
}
package day0705;
public class Person {
String name;
int age;
String gender;
public Person() {
System.out.println("person无参");
}
public Person(String name, int age, String gender) {
this.name = name;
this.age = age;
this.gender = gender;
System.out.println("person全参");
}
public String toString()
{
return name+","+gender+","+age;
}
}