Java-Java编程思想第四版 第九章 练习

练习

abstract class A{
abstract void print();
public A(){print();}
}
public class Ja9_1_3 extends A{
int i=5;
void print(){
System.out.println(i);
}
public static void main(String[] args){
Ja9_1_3 j=new Ja9_1_3();
j.print();
}
}
/*
*output:
0
5
* */

练习4：import static net.mindview.util.Print.*;abstract class Dad {}class Son extends Dad {protected void print() { System.out.println("Son"); }}abstract class SecondDad {abstract protected void print();}class SecondSon extends SecondDad {protected void print() { System.out.println("SecondSon"); }}public class Ja9_1_4 {public static void testPrint(Dad d) {((Son)d).print();//it's necessary}public static void secondTestPrint(SecondDad sd) {sd.print();//don't need ((SecondSon)sd)}public static void main(String[] args) {Son s = new Son();Ja9_1_4.testPrint(s);SecondSon ss = new SecondSon();Ja9_1_4.secondTestPrint(ss);}}练习5：package net.mindview.util;public interface Ja9_2_5b{void first();void second();void third();}import net.mindview.util.Ja9_2_5b;import static net.mindview.util.Print.*;public class Ja9_2_5 implements Ja9_2_5b{public void first(){print("first()");}public void second(){print("second()");}public void third(){print("third()");}public static void main(String[] args){Ja9_2_5 ja=new Ja9_2_5();ja.first();ja.second();ja.third();}}

练习7：import static net.mindview.util.Print.*;public class Ja9_2_7{public static void main(String[] args) {Mouse m=new Mouse();Gerbil[] gb={new Gerbil(m),new Gerbil(m),new Gerbil(m),new Gerbil(m),};for(Gerbil g:gb){g.dispose();}}}interface Rodent{public void hop();public void scurry();public void reproduce();public String toString();}class Mouse implements Rodent{private static int refcount=0;private static int count=0;private final int id=count++;public void refAdd(){refcount++;}protected void dispose(){if(--refcount==0)print("Disposing "+this);}public String toString(){return "Mouse "+id;}public Mouse(){print("Creating "+this);}public void hop() {System.out.println("Mouse hopping");}4000public void scurry() {System.out.println("Mouse scurrying");}public void reproduce() {System.out.println("Making more Mice");}}class Gerbil implements Rodent{private static int count=0;private final int id=count++;private Mouse m;public String toString(){return "Gerbil "+id;}public Gerbil(Mouse m){this.m=m; m.refAdd(); print("Creating "+this);}protected void dispose(){print("Disposing "+this);m.dispose();}public void hop() {System.out.println("Gerbil hopping");}public void scurry() {System.out.println("Gerbil scurrying");}public void reproduce() {System.out.println("Making more Gerbil");}}class Hamster implements Rodent{public void hop() {System.out.println("Hamster hopping");}public void scurry() {System.out.println("Hamster scurrying");}public void reproduce() {System.out.println("Making more Hamster");}public String toString() {return "Hamster";}}

练习8：import static net.mindview.util.Print.*;class Meal {Meal() { print("Meal()"); }}class Bread {Bread() { print("Bread()"); }}class Cheese {Cheese() { print("Cheese()"); }}class Lettuce {Lettuce() { print("Lettuce()"); }}class Lunch extends Meal {Lunch() { print("Lunch()"); }}class PortableLunch extends Lunch {PortableLunch() { print("PortableLunch()");}}interface FastFood{void first();void second();void third();}public class Ja9_2_8 extends PortableLunch implements FastFood{private Bread b = new Bread();private Cheese c = new Cheese();private Lettuce l = new Lettuce();// public Sandwich() { print("Sandwich()"); }public void first(){print("first()");}public void second(){print("second()");}public void third(){print("third()");}public static void main(String[] args) {Ja9_2_8 ja=new Ja9_2_8();ja.first();ja.second();ja.third();}}

练习10：import polymorphism.music.Note;import static net.mindview.util.Print.*;interface Playable{void play(Note n); // Automatically public}interface Instrument {int VALUE = 5; // static & finalvoid adjust();}class Wind implements Instrument,Playable{public void play(Note n) {print(this + ".play() " + n);}public String toString() { return "Wind"; }public void adjust() { print(this + ".adjust()"); }}class Percussion implements Instrument,Playable{public void play(Note n) {print(this + ".play() " + n);}public String toString() { return "Percussion"; }public void adjust() { print(this + ".adjust()"); }}class Stringed implements Instrument,Playable{public void play(Note n) {print(this + ".play() " + n);}public String toString() { return "Stringed"; }public void adjust() { print(this + ".adjust()"); }}class Brass extends Wind {public String toString() { return "Brass"; }}class Woodwind extends Wind {public String toString() { return "Woodwind"; }}public class Ja9_2_10{static void tune(Playable i) {i.play(Note.MIDDLE_C);}static void tuneAll(Playable[] e) {for(Playable i : e)tune(i);}public static void main(String[] args) {Playable[] orchestra = {new Wind(),new Percussion(),new Stringed(),new Brass(),new Woodwind()};tuneAll(orchestra);}}练习11：import interfaces.interfaceprocessor.*;import static net.mindview.util.Print.*;import java.util.*;class A {public String name(){return getClass().getSimpleName();}public String process(Object input){return (String)input;}}class AAdapter implements Processor{A a;public AAdapter(A a){this.a=a;}public String name(){return a.name();}public String process(Object input){return a.process(input);}}class B extends A{public String process(Object input){String m[]=((String)input).split(" ");for(int i=0;i<m.length-1;i=i+2){String temp; temp=m[i];m[i]=m[i+1];m[i+1]=temp;}return Arrays.toString(m);}}public class Ja9_3_11{public static void main(String[] args){String s="Thinking in Java!";Apply.process(new AAdapter(new B()),s);}}/*Using Processor B[in, Thinking, Java!]*/练习12：//: interfaces/Adventure.java// Multiple interfaces.interface CanClim{void play();}interface CanFight {void fight();}interface CanSwim {void swim();}interface CanFly {void fly();}class ActionCharacter {public void fight() {}public void play(){}}class Hero extends ActionCharacterimplements CanFight, CanSwim, CanFly, CanClim{public void swim() {}public void fly() {}}public class Ja9_3_12{public static void t(CanFight x) { x.fight(); }public static void u(CanSwim x) { x.swim(); }public static void v(CanFly x) { x.fly(); }public static void w(ActionCharacter x) { x.fight(); }public static void p(CanClim x){x.play();}public static void main(String[] args) {Hero h = new Hero();t(h); // Treat it as a CanFightu(h); // Treat it as a CanSwimv(h); // Treat it as a CanFlyw(h); // Treat it as an ActionCharacterp(h);}} ///:~练习13：import static net.mindview.util.Print.*;interface A{void aa();}interface B extends A{void bb();}interface C extends A{void cc();}interface D extends B,C{void dd();} //extends can be variablepublic class Ja9_3_13 implements D {public void aa(){print("aa");}public void bb(){print("bb");}public void cc(){print("cc");}public void dd(){print("dd");}public static void main(String[] args){Ja9_3_13 ja=new Ja9_3_13();ja.aa();ja.bb();ja.cc();ja.dd();}}

练习14：import static net.mindview.util.Print.*;interface A{void a1(); void a2();}interface B{void b1(); void b2();}interface C{void c1(); void c2();}interface D extends A,B,C{void d();}public class Ja9_5_14 implements D{public void a1(){print("a1");}public void a2(){print("a2");}public void b1(){print("b1");}public void b2(){print("b2");}public void c1(){print("c1");}public void c2(){print("c2");}public void d(){print("d");}public static void main(String[] args){Ja9_5_14 ja=new Ja9_5_14();ja.a1();ja.a2();ja.b1();ja.b2();ja.c1();ja.c2();ja.d();}}练习15：import static net.mindview.util.Print.*;abstract class A{abstract void a1();abstract void a2();abstract void b1();abstract void b2();abstract void c1();abstract void c2();abstract void d();}public class Ja9_5_15 extends A{void a1(){print("a1");}void a2(){print("a2");}void b1(){print("b1");}void b2(){print("b2");}void c1(){print("c1");}void c2(){print("c2");}void d(){print("d");}public static void main(String[] args){Ja9_5_15 ja=new Ja9_5_15();ja.a1();ja.a2();ja.b1();ja.b2();ja.c1();ja.c2();ja.d();}}练习16：import java.util.*;import java.nio.*;import static net.mindview.util.Print.*;class RandomChars{private static Random rd=new Random();public char next(){return (char)(rd.nextInt(100)+2);}//the way to produce random between [2,100-2+1]; turn int to char}public class Ja9_6_16 extends RandomChars implements Readable{private int count;public Ja9_6_16(int count){this.count=count;}public int read(CharBuffer cb){if(count--==0){return -1;}String result=Character.toString(next())+" ";// method next() can be inferred directly!cb.append(result);return result.length();}public static void main(String[] args){Scanner s=new Scanner(new Ja9_6_16(7));while(s.hasNext()){print(s.next()+" ");//the difference between next() and nextInt()}}}

PS：这一题明确了产生随机数的方法；明确了导出类可以直接调用基类的方法； Scanner的next（）方法比nextInt()等方法更强大；Readable接口的read()方法会被Scanner反复调用直到返回值为-1；产生char的方法是产生int序列，再转型成char序列。练习17：import static net.mindview.util.Print.*;interface A{int a=1,b=2;}public class Ja9_7_17 implements A{public static void main(String[] args){print(a+" "+b);//!a=2;}}

练习18：import static net.mindview.util.Print.*;interface Cycle{void produce();}interface CycleFactory{Cycle getCycle();}class Unicycle implements Cycle{public void produce(){print("it's Unicycle");}}class Bicycle implements Cycle{public void produce(){print("it's Bicycle");}}class Tricycle implements Cycle{public void produce(){print("it's Tricycle");}}class UnicycleFactory implements CycleFactory{public Cycle getCycle(){return new Unicycle();}}class BicycleFactory implements CycleFactory{public Cycle getCycle(){return new Bicycle();}}class TricycleFactory implements CycleFactory{public Cycle getCycle(){return new Tricycle();}}public class Ja9_9_18{static void make(CycleFactory cf){Cycle c=cf.getCycle();c.produce();}public static void main(String[] args){make(new UnicycleFactory());make(new BicycleFactory());make(new TricycleFactory());}}