《 Java 核心技术 》学习笔记
2020-09-17 本文已影响0人
Du1in9
一）Java白皮书
二）基本程序设计结构
移步：https://www.jianshu.com/p/43f45dd0b22f
三）对象与类
- 例1 CalendarTest.java
import java.time.*;
public class CalendarTest
{
public static void main(String[] args)
{
LocalDate date = LocalDate.now();//date = 2020-06-17
int month = date.getMonthValue();//month = 6
int today = date.getDayOfMonth();//today = 17
System.out.println();
System.out.println(date);
date = date.minusDays(today-1);//date = date-16 = 2020-06-01
System.out.println("Mon Tue Wen Thu Fri Sat Sun");
while(date.getMonthValue() == month)
{
System.out.printf("%3d",date.getDayOfMonth());
if(date.getDayOfMonth() == today)
System.out.print("*");
else
System.out.print(" ");
date = date.plusDays(1);//date = date+1
int value = date.getDayOfWeek().getValue();//1 = Monday,...7 = Sunday
if(value == 1) System.out.println();
}
System.out.println();
}
}
- 例2 EmployeeTest.java
import java.time.*;
public class EmployeeTest{
public static void main(String[]args){
Employee[] staff=new Employee[3];
staff[0]=new Employee("Lihua",75000,1989,5,2);
staff[1]=new Employee("Wanggang",65000,1999,6,2);
staff[2]=new Employee("Libai",105000,1979,7,29);
for(Employee e:staff){
e.raiseSalary(5);
}
for(Employee e:staff){
System.out.println("name:"+e.getName());
System.out.println("salary:"+e.getSalary());
System.out.println("hireday:"+e.getHireday()+"\n");
}
}
}
class Employee{
private String name;
private float salary;
private LocalDate hireday;
public Employee(String n,float s,int year,int month,int day){
name=n;
salary=s;
hireday=LocalDate.of(year,month,day);
}
public String getName(){
return name;
}
public float getSalary(){
return salary;
}
public LocalDate getHireday(){
return hireday;
}
public void raiseSalary(double x){
salary*=(1+x/100);
}
}
- 例3 StaticTest.java
public class StaticTest{
public static void main(String[]args){
Employee[] staff=new Employee[3];
staff[0]=new Employee("Lihua",75000);
staff[1]=new Employee("Wanggang",65000);
staff[2]=new Employee("Libai",105000);
for(Employee e:staff){
e.setId();
System.out.println("name:"+e.getName());
System.out.println("salary:"+e.getSalary());
System.out.println("id:"+e.getId());
System.out.println("next id:"+e.getnextId()+"\n");
}
}
}
class Employee{
//静态域nextId
static private int nextId=1;
private String name;
private double salary;
private int id;
public Employee(String n,double s){
name=n;
salary=s;
}
public String getName(){
return name;
}
public double getSalary(){
return salary;
}
public int getId(){
return id;
}
//静态方法
public static int getnextId(){
return nextId;
}
public void setId(){
id=nextId;
nextId++;
}
//静态的main方法
public static void main(String[]args){
Employee e=new Employee("Xiaoming",50000);
System.out.println("name:"+e.getName());
System.out.println("salary:"+e.getSalary());
}
}
// 因为有中文注释，编译命令：>> javac -encoding UTF-8 StaticTest.java
- 例3 ParamTest.java
public class ParamTest{
public static void main(String[]args){
//test1,fail
double percent=10;
System.out.println("before percent:"+percent);
tripleValue(percent);
System.out.println("after percent:"+percent+"\n");
//test2,success
Employee e=new Employee("Lihua",50000);
System.out.println("before salary:"+e.getSalary());
tripleSalary(e);
System.out.println("after salary:"+e.getSalary()+"\n");
//test3,fail
Employee a=new Employee("A",50000);
Employee b=new Employee("B",50000);
System.out.println("before a:"+a.getName()+" b:"+b.getName());
swap(a,b);
System.out.println("after a:"+a.getName()+" b:"+b.getName()+"\n");
}
public static void tripleValue(double percent){
percent*=3;
System.out.println("End percent:"+percent);
}
public static void tripleSalary(Employee x){
x.raiseSalary(200);
System.out.println("End salary:"+x.getSalary());
}
public static void swap(Employee a,Employee b){
Employee temp=a;
a=b;
b=temp;
System.out.println("End a:"+a.getName()+" b:"+b.getName());
}
}
class Employee{
private String name;
private float salary;
public Employee(String n,float s){
name=n;
salary=s;
}
public String getName(){
return name;
}
public float getSalary(){
return salary;
}
public void raiseSalary(double x){
salary*=(1+x/100);
}
}
- 例4 ConstructorTest.java
import java.util.*;
public class ConstructorTest{
public static void main(String[]args){
Employee[] staff=new Employee[3];
staff[0]=new Employee("Harry",40000);
staff[1]=new Employee(60000);
staff[2]=new Employee();
for(Employee e:staff){
System.out.println("name:"+e.getName());
System.out.println("salary:"+e.getSalary());
System.out.println("id:"+e.getId()+"\n");
}
}
}
class Employee{
private static int nextId;
private int id;
private String name="";
private double salary;
//静态初始化块
static {
Random generator=new Random();
nextId=generator.nextInt(10000);//nextId:0~9999
}
{
id=nextId;
nextId++;
}
//对象初始化块
public Employee(String n,double s){
name=n;
salary=s;
}
//用this调用另一个构造器
public Employee(double s){
this("Employee #"+nextId,s);
}
//无参数构造器
public Employee()
{ }
public String getName(){
return name;
}
public double getSalary(){
return salary;
}
public int getId(){
return id;
}
}
- 例5 PackageTest.java
import com.du1in9.Employee;
import static java.lang.System.*;
public class PackageTest{
public static void main(String[]args){
Employee e=new Employee("Lihua",50000,1949,10,1);
e.raiseSalary(5);
out.println("name:"+e.getName());
out.println("salary:"+e.getSalary());
out.println("hireday:"+e.getHireday()+"\n");
}
}
com/du1in9/Employee.java
package com.du1in9;
import java.time.*;
public class Employee{
private String name;
private double salary;
private LocalDate hireday;
public Employee(String n,double s,int year,int month,int day){
name=n;
salary=s;
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 x){
salary*=(1+x/100);
}
}
四）继承
- 例1 inheritance/ManagerTest.java
package inheritance;
public class ManagerTest
{
public static void main(String[] args)
{
Manager boss = new Manager("Carl Cracker", 80000, 1987, 12, 15);
boss.setBonus(5000);
Employee[] staff = new Employee[3];
staff[0] = boss;
staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
staff[2] = new Employee("Tommy Tester", 40000, 1990, 3, 15);
for (Employee e : staff)
System.out.println("name=" + e.getName() + ",salary=" + e.getSalary());
}
}
inheritance/Employee.java
package inheritance;
import java.time.*;
public class Employee
{
private String name;
private double salary;
private LocalDate hireDay;
public Employee(String name, double salary, int year, int month, int day)
{
this.name = name;
this.salary = salary;
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;
}
}
inheritance/Manager.java
package inheritance;
public class Manager extends Employee
{
private double bonus;
public Manager(String name, double salary, int year, int month, int day)
{
super(name, salary, year, month, day);
bonus = 0;
}
public double getSalary()
{
double baseSalary = super.getSalary();
return baseSalary + bonus;
}
public void setBonus(double b)
{
bonus = b;
}
}
- 例2 类，超类，子类 ABC/Employee.java
package ABC;
import java.time.*;
abstract class Person{
public abstract String getDescription();
private String name;
public Person(String n){
this.name = n;
}
public String getName(){
return name;
}
}
class Student extends Person{
private String major;
public Student(String n, String m){
super(n);
this.major = m;
}
public String getDescription(){
return "a student majoring in " + major;
}
}
public class Employee extends Person{
private double salary;
private LocalDate hireDay;
public Employee(String n, double s, int y, int m, int d){
super(n);
this.salary = s;
hireDay = LocalDate.of(y, m, d);
}
public double getSalary(){
return salary;
}
public LocalDate getHireDay(){
return hireDay;
}
public String getDescription(){
return String.format("an employee with a salary of $%.2f", salary);
}
public void raiseSalary(double p){
double raise = salary * p/100;
salary += raise;
}
}
class PersonTest{
public static void main(String[] args){
Person[] people = new Person[2];
people[0] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
people[1] = new Student("Maria Morris", "computer science");
for (Person p : people){
System.out.println(p.getName() + ", " + p.getDescription());
}
}
}
- 例3 equals/Employee.java
import java.time.*;
import java.util.Objects;
public class Employee{
private String name;
private double salary;
private LocalDate hireDay;
public Employee(String n, double s, int y, int m, int d){
this.name = n;
this.salary = s;
hireDay = LocalDate.of(y, m, d);
}
public String getName(){
return name;
}
public double getSalary(){
return salary;
}
public LocalDate getHireDay(){
return hireDay;
}
public void raiseSalary(double p){
double raise = salary * p/100;
salary += raise;
}
public boolean equals(Object o){
if (o == this) return true;
if (o == null) return false;
if (getClass() != o.getClass()) return false;
Employee other = (Employee) o;
return Objects.equals(name, other.name) && salary == other.salary && Objects.equals(hireDay, other.hireDay);
}
public int hashCode(){
return Objects.hash(name, salary, hireDay);
}
public String toString(){
return getClass().getName() + "[ name = " + name + ", salary = " + salary + ", hireDay = " + hireDay + " ]";
}
public static void main(String[] args){
Employee A1 = new Employee("Alice Adams", 75000, 1987, 12, 15);
Employee A2 = A1;
Employee A3 = new Employee("Alice Adams", 75000, 1987, 12, 15);
Employee bob = new Employee("Bob Brandson", 50000, 1989, 10, 1);
System.out.println("A1 == A2: " + (A1 == A2));
System.out.println("A1 == A3: " + (A1 == A3));
System.out.println("A1.equals(A3): " + A1.equals(A3));
System.out.println("A1.equals(bob): " + A1.equals(bob));
System.out.println("bob.toString(): " + bob);
Manager carl = new Manager("Carl Cracker", 80000, 1987, 12, 15);
Manager boss = new Manager("Carl Cracker", 80000, 1987, 12, 15);
boss.setBonus(5000);
System.out.println("boss.toString(): " + boss);
System.out.println("carl.equals(boss): " + carl.equals(boss));
System.out.println("A1.hashCode(): " + A1.hashCode());
System.out.println("A3.hashCode(): " + A3.hashCode());
System.out.println("bob.hashCode(): " + bob.hashCode());
System.out.println("carl.hashCode(): " + carl.hashCode());
}
}
class Manager extends Employee{
private double bonus;
public Manager(String n, double s, int y, int m, int d){
super(n, s, y, m, d);
bonus = 0;
}
public double getSalary(){
double baseSalary = super.getSalary();
return baseSalary + bonus;
}
public void setBonus(double b){
this.bonus = b;
}
public boolean equals(Object o){
if (!super.equals(o)) return false;
Manager other = (Manager) o;
return bonus == other.bonus;
}
public int hashCode(){
return super.hashCode() + 17 * new Double(bonus).hashCode();
}
public String toString(){
return super.toString() + "[ bonus = " + bonus + " ]";
}
}
- 例4 arrayList/ArrayListTest.java
package arrayList;
import java.time.LocalDate;
import java.util.ArrayList;
class Employee{
private String name;
private double salary;
private LocalDate hireDay;
// 构造函数
public Employee(String n, double s, int y, int m, int d){
this.name = n;
this.salary = s;
hireDay = LocalDate.of(y, m, d);
}
// 得到名字
public String getName(){
return name;
}
// 发薪日期
public double getSalary(){
return salary;
}
// 雇用日期
public LocalDate getHireDay(){
return hireDay;
}
// 加薪日期
public void raiseSalary(double p){
double raise = salary * p/100;
salary += raise;
}
}
public class ArrayListTest{
public static void main(String[] args){
ArrayList<Employee> staff = new ArrayList<>();
staff.add(new Employee("Carl Cracker", 75000, 1987, 12, 15));
staff.add(new Employee("Harry Hacker", 50000, 1989, 10, 1));
staff.add(new Employee("Tony Tester", 40000, 1990, 3, 15));
// for each 循环
for (Employee e : staff){
e.raiseSalary(5);
}
for (Employee e : staff){
System.out.println("name = " + e.getName() + ", salary = " + e.getSalary() + ", hireDay = " + e.getHireDay());
}
}
}
- 例5 enums/EnumTest.java
package enums;
import java.util.*;
public class EnumTest{
public static void main(String[] args){
Scanner in = new Scanner(System.in);
System.out.print("Enter a size: (small, medium, large, extra_large) ");
// 将输入字符串转换为大写
String input = in.next().toUpperCase();
Size s = Enum.valueOf(Size.class, input);
// 输出尺寸
System.out.println("size = " + s);
// 输出尺寸缩写
System.out.println("abbreviation = " + s.get());
if (s == Size.extra_large){ System.out.println("Good job!"); }
}
}
enum Size{
small("S"), medium("M"), large("L"), extra_large("XL");
private Size(String a){ this.abbreviation = a; }
public String get(){ return abbreviation; }
// abbreviation：缩写
private String abbreviation;
}
- 例6 reflection/ReflectionTest.java
package reflection;
import java.util.*;
import java.lang.reflect.*;
public class ReflectionTest{
public static void main(String[] args){
String name;
if (args.length > 0) name = args[0];
else{
Scanner in = new Scanner(System.in);
System.out.println("Enter class name (e.g. java.util.Date): ");
name = in.next();
}
try{
Class cl = Class.forName(name);
Class supercl = cl.getSuperclass();
String modifiers = Modifier.toString(cl.getModifiers());
if (modifiers.length() > 0) System.out.print(modifiers + " ");
System.out.print("class " + name);
if (supercl != null && supercl != Object.class) System.out.print(" extends " + supercl.getName());
System.out.print("\n{\n");
printConstructors(cl);
System.out.println();
printMethods(cl);
System.out.println();
printFields(cl);
System.out.println("}");
}
catch (ClassNotFoundException e){
e.printStackTrace();
}
System.exit(0);
}
public static void printConstructors(Class cl){
Constructor[] constructors = cl.getDeclaredConstructors();
for (Constructor c : constructors){
String name = c.getName();
System.out.print(" ");
String modifiers = Modifier.toString(c.getModifiers());
if (modifiers.length() > 0) System.out.print(modifiers + " ");
System.out.print(name + "(");
Class[] paramTypes = c.getParameterTypes();
for (int j = 0; j < paramTypes.length; j++){
if (j > 0) System.out.print(", ");
System.out.print(paramTypes[j].getName());
}
System.out.println(");");
}
}
public static void printMethods(Class cl){
Method[] methods = cl.getDeclaredMethods();
for (Method m : methods){
Class retType = m.getReturnType();
String name = m.getName();
System.out.print(" ");
String modifiers = Modifier.toString(m.getModifiers());
if (modifiers.length() > 0) System.out.print(modifiers + " ");
System.out.print(retType.getName() + " " + name + "(");
Class[] paramTypes = m.getParameterTypes();
for (int j = 0; j < paramTypes.length; j++){
if (j > 0) System.out.print(", ");
System.out.print(paramTypes[j].getName());
}
System.out.println(");");
}
}
public static void printFields(Class cl){
Field[] fields = cl.getDeclaredFields();
for (Field f : fields){
Class type = f.getType();
String name = f.getName();
System.out.print(" ");
String modifiers = Modifier.toString(f.getModifiers());
if (modifiers.length() > 0) System.out.print(modifiers + " ");
System.out.println(type.getName() + " " + name + ";");
}
}
}
- 例7 ObjectAnalyzerTest.java
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
class ObjectAnalyzer{
private ArrayList<Object> x = new ArrayList<>();
public String toString(Object o){
if (o == null) return " null ";
if (x.contains(o)) return " ... ";
x.add(o);
Class cl = o.getClass();
if (cl == String.class) return (String) o;
if (cl.isArray()){
String r = cl.getComponentType() + " []{ ";
for (int i = 0; i < Array.getLength(o); i++){
if (i > 0) r += " , ";
Object y = Array.get(o, i);
if (cl.getComponentType().isPrimitive()) r += y;
else r += toString(y);
}
return r + "}";
}
String r = cl.getName();
do{
r += "[";
Field[] fields = cl.getDeclaredFields();
AccessibleObject.setAccessible(fields, true);
for (Field f : fields){
if (!Modifier.isStatic(f.getModifiers())){
if (!r.endsWith("[")) r += ",";
r += f.getName() + "=";
try{
Class t = f.getType();
Object y = f.get(o);
if (t.isPrimitive()) r += y;
else r += toString(y);
}
catch (Exception e){
e.printStackTrace();
}
}
}
r += "]";
cl = cl.getSuperclass();
}
while (cl != null);
return r;
}
}
public class ObjectAnalyzerTest{
public static void main(String[] args){
ArrayList<Integer> s = new ArrayList<>();
for (int i = 1; i <= 5; i++)
s.add(i * i);
System.out.println(new ObjectAnalyzer().toString(s));
}
}
- 例8 CopyOfTest.java
import java.lang.reflect.*;
import java.util.*;
public class CopyOfTest{
public static void main(String[] args){
int[] a = { 1, 2, 3 };
a = (int[]) goodCopyOf(a, 10);
System.out.println(Arrays.toString(a));
String[] b = { "Tom", "Dick", "Harry" };
b = (String[]) goodCopyOf(b, 10);
System.out.println(Arrays.toString(b));
System.out.println("The following call will generate an exception.");
b = (String[]) badCopyOf(b, 10);
}
public static Object[] badCopyOf(Object[] a, int L){
Object[] newArray = new Object[L];
System.arraycopy(a, 0, newArray, 0, Math.min(a.length, L));
return newArray;
}
public static Object goodCopyOf(Object a, int L){
Class cl = a.getClass();
if (!cl.isArray()) return null;
Class componentType = cl.getComponentType();
int length = Array.getLength(a);
Object newArray = Array.newInstance(componentType, L);
System.arraycopy(a, 0, newArray, 0, Math.min(length, L));
return newArray;
}
}
- 例9 M.java
import java.lang.reflect.*;
public class M{
public static void main(String[] args) throws Exception{
Method square = M.class.getMethod("square", double.class);
Method sqrt = Math.class.getMethod("sqrt", double.class);
print(1, 10, 10, square);
print(1, 10, 10, sqrt);
}
public static double square(double x){
return x * x;
}
// f 是 Method 类对象
public static void print(double A, double B, int n, Method f){
System.out.println(f);
double dx = (B - A) / (n - 1);
for (double x = A; x <= B; x += dx){
// try catch throw 异常机制
try{
// invoke 调用本类的静态方法
double y = (Double) f.invoke(null, x);
System.out.printf("%10.4f | %10.4f%n", x, y);
}
catch (Exception e){
e.printStackTrace();
}
}
}
}
五）接 口，lambda 表达式，内部类
- 例1 EmployeeSortTest.java
import java.util.*;
class Employee implements Comparable<Employee>{
private String name;
private double salary;
// 构造函数
public Employee(String n, double s){
this.name = n;
this.salary = s;
}
public String getName(){
return name;
}
public double getSalary(){
return salary;
}
// 覆盖 Comparable 中的抽象方法 compareTo(Employee)
public int compareTo(Employee o){
return Double.compare(salary, o.salary);
}
}
public class EmployeeSortTest{
public static void main(String[] args){
Employee[] e = new Employee[3];
e[0] = new Employee("Harry Hacker", 35000);
e[1] = new Employee("Carl Cracker", 75000);
e[2] = new Employee("Tony Tester", 38000);
// 工资排序
Arrays.sort(e);
for (Employee x : e)
System.out.println("name = " + x.getName() + ", salary=" + x.getSalary());
}
}
- 例2 TimerTest.java
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.Timer;
public class TimerTest{
public static void main(String[] args){
ActionListener l = new Time();
// 第一个参数时间间隔，第二个参数监听器对象
Timer t = new Timer(10000, l);
t.start();
JOptionPane.showMessageDialog(null, "Quit program?");
System.exit(0);
}
}
class Time implements ActionListener{
public void actionPerformed(ActionEvent event){
System.out.println("Time: " + new Date());
Toolkit.getDefaultToolkit().beep();
}
}
- 例3 CloneTest.java
import java.util.Date;
import java.util.GregorianCalendar;
class Employee implements Cloneable{
private String name;
private double salary;
private Date hireDay;
public Employee(String n, double s){
this.name = n;
this.salary = s;
hireDay = new Date();
}
public Employee clone() throws CloneNotSupportedException{
Employee c = (Employee) super.clone();
c.hireDay = (Date) hireDay.clone();
return c;
}
public void setHireDay(int y, int m, int d){
Date x = new GregorianCalendar(y, m - 1, d).getTime();
hireDay.setTime(x.getTime());
}
public void raiseSalary(double p){
double raise = salary * p/100;
salary += raise;
}
//////////////////////////
public String toString(){
return "Employee [ name = " + name + " , salary = " + salary + " , hireDay = " + hireDay + " ]";
}
//////////////////////////
}
public class CloneTest{
public static void main(String[] args){
try{
Employee a = new Employee("John Q. Public", 50000);
a.setHireDay(2000, 1, 1);
Employee b = a.clone();
b.raiseSalary(10);
b.setHireDay(2002, 12, 31);
System.out.println("a = " + a);
System.out.println("b = " + b);
}
catch (CloneNotSupportedException e){
e.printStackTrace();
}
}
}
- 例4 LambdaTest.java
import java.util.*;
import javax.swing.*;
import javax.swing.Timer;
public class LambdaTest{
public static void main(String[] args){
String[] p = new String[] { "Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune" };
System.out.println(Arrays.toString(p));
System.out.println("Sorted in order: ");
Arrays.sort(p);
System.out.println(Arrays.toString(p));
System.out.println("Sorted by length: ");
Arrays.sort(p, (first, second) -> first.length() - second.length());
System.out.println(Arrays.toString(p));
// 1000ms = 1s
Timer t = new Timer(1000, event -> System.out.println("The time is: " + new Date()));
t.start();
JOptionPane.showMessageDialog(null, "Quit program?");
System.exit(0);
}
}
- 例5 InnerClassTest.java
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.Timer;
public class InnerClassTest{
public static void main(String[] args){
Talk c = new Talk(1000, true);
c.start();
JOptionPane.showMessageDialog(null, "Quit program ?");
System.exit(0);
}
}
class Talk{
private int interval;
private boolean beep;
public Talk(int i, boolean b){
this.interval = i;
this.beep = b;
}
public void start(){
ActionListener x = new Printer();
Timer t = new Timer(interval, x);
t.start();
}
public class Printer implements ActionListener{
public void actionPerformed(ActionEvent event){
System.out.println("Time: " + new Date());
if (beep) Toolkit.getDefaultToolkit().beep();
}
}
}
- 例6 AnonymousInnerClassTest.java
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.Timer;
public class AnonymousInnerClassTest{
public static void main(String[] args){
Talk c = new Talk();
c.start(1000, true);
JOptionPane.showMessageDialog(null, "Quit program ?");
System.exit(0);
}
}
class Talk{
public void start(int interval, boolean beep){
ActionListener l = new ActionListener(){
public void actionPerformed(ActionEvent event){
System.out.println("Time: " + new Date());
if (beep) Toolkit.getDefaultToolkit().beep();
}
};
Timer t = new Timer(interval, l);
t.start();
}
}
- 例7 StaticInnerClassTest.java
public class StaticInnerClassTest{
public static void main(String[] args){
double[] d = new double[10];
for (int i = 0; i < d.length; i++){
d[i] = 100 * Math.random();
System.out.println(d[i]);
}
Array.Pair p = Array.minmax(d);
System.out.println("min = " + p.getA());
System.out.println("max = " + p.getB());
}
}
class Array{
public static class Pair{
private double A;
private double B;
public Pair(double a, double b){
A = a;
B = b;
}
public double getA(){
return A;
}
public double getB(){
return B;
}
}
public static Pair minmax(double[] V){
double min = Double.POSITIVE_INFINITY;
double max = Double.NEGATIVE_INFINITY;
for (double v : V){
if (min > v) min = v;
if (max < v) max = v;
}
return new Pair(min, max);
}
}
- 例8 ProxyTest.java
import java.lang.reflect.*;
import java.util.*;
public class ProxyTest{
public static void main(String[] y){
Object[] m = new Object[1000];
for (int i = 0; i < m.length; i++){
Integer x = i + 1;
InvocationHandler h = new Trace(x);
Object proxy = Proxy.newProxyInstance(null, new Class[] { Comparable.class } , h);
m[i] = proxy;
}
Integer key = new Random().nextInt(m.length) + 1;
int result = Arrays.binarySearch(m, key);
if (result >= 0) System.out.println( m[result] );
}
}
class Trace implements InvocationHandler{
private Object target;
public Trace(Object t){
target = t;
}
public Object invoke(Object proxy, Method m, Object[] y) throws Throwable{
System.out.print(target);
System.out.print("." + m.getName() + "(");
if (y != null){
for (int i = 0; i < y.length; i++){
System.out.print(y[i]);
if (i < y.length - 1) System.out.print(", ");
}
}
System.out.println(")");
return m.invoke(target, y);
}
}
