java编程思想第四版第十四章 类型信息习题

2021/6/4 14:20:53

编程Tag： string class Java net 类型信息 public 习题 typeinfo mindview

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  3. 第三题u 
    package net.mindview.typeinfo.test4;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

abstract class Shape {
    void draw(){
        /*
         * 重点在这里: 
         * this指代的是实例对象,由于使用+连接字符串, 会自动调用对象的toString()方法.
         */
        System.out.println(this + ".draw()");
    }
    
    public abstract String toString();
}

class Circle extends Shape{
    @Override
    public String toString() {
        return "Circle";
    }
}

class Square extends Shape{
    @Override
    public String toString() {
        return "Square";
    }
}

class Triangle extends Shape{
    @Override
    public String toString() {
        return "Triangle";
    }
}

//菱形
class Rhomboid extends Shape{
    @Override
    public String toString() {
        return "Rhomboid";
    }
}

public class Shapes {

    
    public static void main(String[] args) {
        List<Shape> shapes = new ArrayList<Shape>(Arrays.asList(
            new Circle(), new Square(), new Triangle(), new Rhomboid()));
        
        for(Shape shape:shapes){
            shape.draw();
        }
        
        for(int i=0;i<shapes.size(); i++){
            Shape shape = shapes.get(i);
            if(i == 3){
                Rhomboid r = (Rhomboid)shape;
                Circle c = (Circle)shape;
            }
        }
    }
                                                              }

    运行结果:

    Circle.draw()
Square.draw()
Exception in thread "main" Triangle.draw()
Rhomboid.draw()
java.lang.ClassCastException: net.mindview.typeinfo.test4.Rhomboid cannot be cast to net.mindview.typeinfo.test4.Circle
    at net.mindview.typeinfo.test4.Shapes.main(Shapes.java:63)

    不可以向下转型到Circle

  4. 第四题

    package net.mindview.typeinfo.test4;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

abstract class Shape {
    void draw(){
        /*
         * 重点在这里: 
         * this指代的是实例对象,由于使用+连接字符串, 会自动调用对象的toString()方法.
         */
        System.out.println(this + ".draw()");
    }
    
    public abstract String toString();
}

class Circle extends Shape{
    @Override
    public String toString() {
        return "Circle";
    }
}

class Square extends Shape{
    @Override
    public String toString() {
        return "Square";
    }
}

class Triangle extends Shape{
    @Override
    public String toString() {
        return "Triangle";
    }
}

//菱形
class Rhomboid extends Shape{
    @Override
    public String toString() {
        return "Rhomboid";
    }
}

public class Shapes {
    public static void main(String[] args) {
        List<Shape> shapes = new ArrayList<Shape>(Arrays.asList(
            new Circle(), new Square(), new Triangle(), new Rhomboid()));
        
        for(Shape shape:shapes){
            shape.draw();
        }
        
        for(int i=0;i<shapes.size(); i++){
            Shape shape = shapes.get(i);
            if(i == 3){
                //添加instanceof判断
                if (shape instanceof Rhomboid){
                    Rhomboid r = (Rhomboid)shape;
                }
                if(shape instanceof Circle){
                    Circle c = (Circle)shape;
                }
            }
        }
    }
                                                              }

     

    使用Class.newInstance方法,必须有一个无参构造方法

  5. 第五题: 
    package net.mindview.typeinfo;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

abstract class Shape {
    void draw(){
        /*
         * 重点在这里: 
         * this指代的是实例对象,由于使用+连接字符串, 会自动调用对象的toString()方法.
         */
        System.out.println(this + ".draw()");
    }
    
    void rotate(){
        Class<? extends Shape> clazz = this.getClass();
        if(!clazz.getSimpleName().equals("Circle")){
            System.out.println("旋转"+ this);
        }else{
            System.out.println(this+"不需要旋转");
        }
    }
    
    public abstract String toString();
}

class Circle extends Shape{
    @Override
    public String toString() {
        return "Circle";
    }
}

class Square extends Shape{
    @Override
    public String toString() {
        return "Square";
    }
}

class Triangle extends Shape{
    @Override
    public String toString() {
        return "Triangle";
    }
}

//菱形
class Rhomboid extends Shape{
    @Override
    public String toString() {
        return "Rhomboid";
    }
}

public class Shapes {

    
    public static void main(String[] args) {
        List<Shape> shapes = new ArrayList<Shape>(Arrays.asList(
            new Circle(), new Square(), new Triangle(), new Rhomboid()));
        
        for(Shape shape:shapes){
            shape.draw();
            shape.rotate();
        }
        
        /*for(int i=0;i<shapes.size(); i++){
            Shape shape = shapes.get(i);
            if(i == 3){
                Rhomboid r = (Rhomboid)shape;
                Circle c = (Circle)shape;
            }
        }*/
    }
                                                              }

     

  7. 第七题 
    package net.mindview.typeinfo.test8;

import java.util.HashSet;
import java.util.Set;

interface A {}
interface B {}
interface C {}

class D implements B{
    private int di=0;
    private String dname="";
    static{
        System.out.println("this is D");
        
    }
}

class E extends D implements A, B, C{
    private int ei=0;
    private String ename="";
    static{
        System.out.println("this is E");
        
    }
}

class F extends E implements A {
    private int fi=0;
    private String fname="";
    static{
        System.out.println("this is F");
        
    }
}
/**
 * 接受任意对象作为参数, 递归打印出该对象继承体系中所有的的类.
 * 包括继承的父类, 和实现的接口
 * 
 * 分析: 一个类智能继承一个父类, 可以实现多个接口.
 * 父类可以继承一个类,实现多个接口. 实现的接口可能和子类重复, 因此需要去重.
 * 递归实现
 * @author samsung
 *
 */
class G {
    public void printSuperClass(Class c){
        if(c == null) return ;
        
        System.out.println(c.getName());
        
        //得到这个类的接口
        Class[] interfaces = c.getInterfaces();
        
        for(Class interfaceClass:interfaces){
            printSuperClass(interfaceClass);
        }
        printSuperClass(c.getSuperclass());
    }
}

public class Test8 {
    public static void main(String[] args) {
        G g = new G();
        g.printSuperClass(F.class);
    }
}

    运行结果:

    net.mindview.typeinfo.test8.F
net.mindview.typeinfo.test8.A
net.mindview.typeinfo.test8.E
net.mindview.typeinfo.test8.A
net.mindview.typeinfo.test8.B
net.mindview.typeinfo.test8.C
net.mindview.typeinfo.test8.D
net.mindview.typeinfo.test8.B
java.lang.Object

     

  8. 第八题 
    package net.mindview.typeinfo.test8;

interface A {}
interface B {}
interface C {}

class D {
    static{
        System.out.println("this is D");
        
    }
}

class E extends D implements A, B, C{
    static{
        System.out.println("this is E");
        
    }
}

class F extends E {
    static{
        System.out.println("this is F");
        
    }
}

class G {
    public void printSuperClass(Class c){
        Class upClass = c.getSuperclass();
        
        try {
            System.out.println(upClass.newInstance());
        } catch (InstantiationException e) {
            System.out.println("实例化Instance 失败");
            System.exit(1);
        } catch (IllegalAccessException e) {
            System.out.println("实例化Instance 失败");
            System.exit(1);
        }
        if(upClass.getSuperclass() != null ){
            printSuperClass(upClass);
        }
    }
}

public class Test8 {
    public static void main(String[] args) {
        G g = new G();
        g.printSuperClass(F.class);
    }
}

    运行结果:

    this is D
this is E
net.mindview.typeinfo.test8.E@17cb0a16
net.mindview.typeinfo.test8.D@1303368e
java.lang.Object@37f2ae62

     

  9. 第九题 
    package net.mindview.typeinfo.test9;

import java.lang.reflect.Field;

interface A {}
interface B {}
interface C {}

class D {
    public int i=0;
    public String name="";
    static{
        System.out.println("this is D");
        
    }
}

class E extends D implements A, B, C{
    public int i=0;
    public String name="";
    static{
        System.out.println("this is E");
        
    }
}

class F extends E {
    public int i=0;
    public String name="";
    static{
        System.out.println("this is F");
        
    }
}

class G {
    public void printSuperClass(Class c){
        Class upClass = c.getSuperclass();
        try {
            //获取类中的字段
            Field[] fs = upClass.getDeclaredFields();
            System.out.println(fs.length);
            for(Field f:fs){
                //打印字段名
                System.out.println(f.getName());
                //获取字段值
                Object value = upClass.getDeclaredField(f.getName());
                System.out.println(value);
            }
        } catch (Exception e1) {
            e1.printStackTrace();
        }
        
        try {
            System.out.println(upClass.newInstance());
        } catch (InstantiationException e) {
            System.out.println("实例化Instance 失败");
            System.exit(1);
        } catch (IllegalAccessException e) {
            System.out.println("实例化Instance 失败");
            System.exit(1);
        }
        if(upClass.getSuperclass() != null ){
            printSuperClass(upClass);
        }
    }
}

public class Test9 {
    public static void main(String[] args) {
        G g = new G();
        g.printSuperClass(F.class);
    }
}

    运行结果:

    2
i
public int net.mindview.typeinfo.test9.E.i
name
public java.lang.String net.mindview.typeinfo.test9.E.name
this is D
this is E
net.mindview.typeinfo.test9.E@1440578d
2
i
public int net.mindview.typeinfo.test9.D.i
name
public java.lang.String net.mindview.typeinfo.test9.D.name
net.mindview.typeinfo.test9.D@26f04d94
0
java.lang.Object@38a3c5b6

     

  10. 第十题 
    package net.mindview.typeinfo.test10;
class Pot{}
public class  Test10 {
    public static void judgeType(Object c){
        Class arrType = c.getClass().getComponentType();
        System.out.println(arrType.getName());
    }
    public static void main(String[] args) {
        judgeType(new char[10]);
        judgeType(new String[10]);
        judgeType(new long[10]);
        judgeType(new boolean[10]);
        judgeType(new Pot[10]);
        
    }

}

    运行结果:

    char
java.lang.String
long
boolean
net.mindview.typeinfo.test10.Pot

     

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  14. 第十四题 
    package net.mindview.typeinfo.test14;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Random;

import net.mindview.typeinfo.factory.Factory;

/**
 *  部件类
 *  
 *  比如: 有过滤器部件, 皮带部件等. 
 *  空气净化器中需要有过滤器部件, 因此要有一个制造空气净化器的过滤器的工厂
 *  汽车尾气净化器也需要有过滤器部件, 因此需要一个制造汽车尾气的过滤器的工厂
 *  
 *  皮带
 *  车轮需要皮带, 因此需要一个制造车轮的皮带的工厂
 * @author samsung
 *
 */
class Part{
    @Override
    public String toString() {
        return this.getClass().getSimpleName();
    }
    
    //目前已注册的部件工厂
    static List<String> partNames = Arrays.asList(
            "net.mindview.typeinfo.test14.FuelFilter",
            "net.mindview.typeinfo.test14.AirFilter",
            "net.mindview.typeinfo.test14.CabinFilter",
            "net.mindview.typeinfo.test14.OilFilter",
            "net.mindview.typeinfo.test14.FanBelt",
            "net.mindview.typeinfo.test14.GeneratorBelt",
            "net.mindview.typeinfo.test14.PowerSteeringBelt"
            
        );
    static{
        
    }
    
    private static Random rand = new Random(47);
    
    //随机得到一个已注册的部件工厂, 并制造部件
    public static Part createRandom(){
        int n = rand.nextInt(partNames.size());
        try {
            return (Part) Class.forName(partNames.get(n)).newInstance();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return null;
    }
}

//过滤器部件
class Filter extends Part {
    
}

//燃料过滤器部件
class FuelFilter extends Filter {
    public static class Factory implements net.mindview.typeinfo.factory.Factory<FuelFilter>{

        @Override
        public FuelFilter create() {
            return new FuelFilter();
        }
    }
}

//空气净化器部件
class AirFilter extends Filter {
    public static class Factory implements net.mindview.typeinfo.factory.Factory<AirFilter>{
        @Override
        public AirFilter create() {
            return new AirFilter();
        }
    }
}

//机舱空气过滤器部件
class CabinFilter extends Filter {
    public static class Factory implements net.mindview.typeinfo.factory.Factory<CabinFilter>{
        @Override
        public CabinFilter create() {
            return new CabinFilter();
        }
    }
}

//燃油过滤器部件
class OilFilter extends Filter {
    public static class Factory implements net.mindview.typeinfo.factory.Factory<OilFilter>{
        @Override
        public OilFilter create() {
            return new OilFilter();
        }
    }
}

//皮带部件
class Belt extends Part{}

//风扇皮带部件
class FanBelt extends Belt {
    public static class Factory implements net.mindview.typeinfo.factory.Factory<FanBelt>{
        @Override
        public FanBelt create() {
            return new FanBelt();
        }
    }
}

//发动机皮带部件
class GeneratorBelt extends Belt {
    public static class Factory implements net.mindview.typeinfo.factory.Factory<GeneratorBelt>{
        @Override
        public GeneratorBelt create() {
            return new GeneratorBelt();
        }
    }
}

//转向动力装置皮带部件
class PowerSteeringBelt extends Belt {
    public static class Factory implements net.mindview.typeinfo.factory.Factory<PowerSteeringBelt>{
        @Override
        public PowerSteeringBelt create() {
            return new PowerSteeringBelt();
        }
    }
}


/**
 * 查询目前已注册的工厂类
 * @author samsung
 *
 */
public class RegisteredFactories {

    public static void main(String[] args) {
        for(int i=0;i<10;i++){
            System.out.println(Part.createRandom());
            
        }

    }

}

     

  15. 第十五题: 内容太多, 直接参考demo
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  18. 第十八题: 
    package net.mindview.typeinfo;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.regex.Pattern;

public class ShowMethods {
    private ShowMethods(){}
    private static String usage = ""
            + "usage:\n"
            + "ShowMethods qualified.class.name\n"
            + "To show all methods in class or:\n"
            + "ShowMethods qualified.class.name. word\n"
            + "To search for methodds invoiving 'word'";
    
    private static Pattern p = Pattern.compile("\\w+\\.");
    public static void main(String[] args) {
        if(args.length<1){
            System.out.println(usage);
            System.exit(1);
        }
        
        int lines = 0; 
        try {
            Class<?> c = Class.forName(args[0]);
            //getMethods获取的是整个继承树中所有的方法
            Method[] methods = c.getMethods();
            //获取已有的构造器
            Constructor[] ctors = c.getConstructors();
            
            if(args.length == 1){
                //打印所有继承树中的方法名
                for(Method method: methods){
                    System.out.println(p.matcher(method.toString()).replaceAll(""));
                }
                //打印全部构造器
                for(Constructor ctor: ctors){
                    System.out.println(p.matcher(ctor.toString()).replaceAll(""));
                }
                lines = methods.length + ctors.length;
            }else {
                //打印指定类中的方法
                for(Method method: methods){
                    if(method.toString().indexOf(args[1]) != -1){
                        System.out.println(p.matcher(method.toString()).replaceAll(""));
                        lines++;
                    }
                }
                //打印构造器
                for(Constructor ctor :ctors){
                    if(ctor.toString().indexOf(args[1])!=-1){
                        System.out.println(p.matcher(ctor.toString()).replaceAll(""));
                        lines++;
                    }
                }
            }
            
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

}

     

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