Java - Thinking in Java 第7章 习题

1

/** * 惰性初始化 * <p/> * Created by wang on 15/8/6. */class Init {    public Init() {        System.out.println("Init init");    }}public class LazyInit {    Init init;    @Override    public String toString() {        System.out.println("Print");        init = new Init();        return super.toString();    }    public static void main(String[] arg) {        System.out.println(new LazyInit());    }}/** * Output: Print Init init LazyInit@a3901c6 */

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2

/** * 继承 * <p/> * Created by wang on 15/8/7. */class Cleaner {    private String s = "Cleaner";    public static void main(String[] args) {        Cleaner x = new Cleaner();        x.dilute().apply().scrub();        System.out.println(x);    }    public void append(String a) {        s += a;    }    public Cleaner dilute() {        append(" dilute");        return this;    }    public Cleaner apply() {        append(" apply");        return this;    }    public Cleaner scrub() {        append(" scrub");        return this;    }    @Override    public String toString() {        return s;    }}class Detergent extends Cleaner {    public static void main(String[] args) {        Detergent d = new Detergent();        ((Detergent) d.dilute().apply()).scrub().foam();        System.out.println(d);    }    @Override    public Detergent scrub() {        append(" Detergent: scrub()");        super.scrub();        return this;    }    public Detergent foam() {        append(" foam");        return this;    }}public class Disinfectant extends Detergent {    public static void main(String[] args) {        Disinfectant d = new Disinfectant();        ((Disinfectant) d.dilute().apply()).scrub().sterilize();        System.out.println(d);        Detergent.main(args);        Cleaner.main(args);    }    @Override    public Disinfectant scrub() {        append(" Disinfectant: scrub()");        super.scrub();        return this;    }    public Disinfectant sterilize() {        append(" sterilize");        return this;    }}/** * Output: Cleaner dilute apply Disinfectant: scrub() Detergent: scrub() scrub sterilize Cleaner dilute apply Detergent: scrub() scrub foam Cleaner dilute apply scrub */

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3

/** * 默认构造器 * <p/> * Created by wang on 15/8/7. */class Art {    public void show() {        System.out.println("show");    }}class Drawing extends Art {    public void draw() {        System.out.println("draw");    }}public class Cartoon extends Drawing {    public void play() {        System.out.println("play");    }    public static void main(String[] args) {        Cartoon c = new Cartoon();        c.show();        c.draw();        c.play();    }}

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4

/** * 基类构造器 * <p/> * Created by wang on 15/8/7. */class Art {    public Art(String author) {        System.out.println("Art:" + author);    }}class Drawing extends Art {    public Drawing(String author) {        super(author);        System.out.println("Drawing:" + author);    }}public class Cartoon extends Drawing {    public Cartoon(String author) {        super(author);        System.out.println("Cartoon:" + author);    }    public static void main(String[] args) {        new Cartoon("Caroline");    }}/** * Output: Art:Caroline Drawing:Caroline Cartoon:Caroline */

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5

/** * 构造函数先于其他函数调用. * <p/> * Created by wang on 15/8/7. */class A {    public A() {        System.out.println("A");    }}class B {    public B() {        System.out.println("B");    }}class C extends A {    private B mB = new B();}public class Cross {    public static void main(String[] args) {        C c = new C();    }}/** * Output: A B */

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6

报错: 对super的调用必须是构造函数中的第一个语句.

/** * 带参数的构造器 * <p/> * Created by wang on 15/8/8. */class Game {    Game(int i) {        System.out.println("Game Constructor:" + i);    }}class BoardGame extends Game {    BoardGame(int i) {        super(i);        System.out.println("BoardGame Constructor:" + i);    }}public class Chess extends BoardGame {    public Chess() {        super(11);        System.out.println("Chess Constructor");//        super(11); // 报错    }    public static void main(String[] args) {        new Chess();    }}/** * 报错: 对super的调用必须是构造函数中的第一个语句 */

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7

/** * 继承带参数的构造器 * <p/> * Created by wang on 15/8/7. */class A {    public A(String s) {        System.out.println("A:" + s);    }}class B {    public B(String s) {        System.out.println("B:" + s);    }}class C extends A {    public C(String s) {        super(s);    }    private B mB = new B("Caroline");}public class Cross {    public static void main(String[] args) {        new C("Wendy");    }}/** * Output: A:Wendy B:Caroline */

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8

/** * 构造器 * Created by wang on 15/8/8. */class Haha {    public Haha(String s) {        System.out.println(s + ": Haha");    }}public class DConstructor extends Haha {    public DConstructor() {        this("Caroline");    }    public DConstructor(String s) {        super(s);    }    public static void main(String[] args) {        new DConstructor();    }}/** * Output: * Caroline: Haha */

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9

/** * 派生类自动创建基类的成员变量 * <p/> * Created by wang on 15/8/8. */class Component1 {    public Component1() {        System.out.println("Component1");    }}class Component2 {    public Component2() {        System.out.println("Component2");    }}class Component3 {    public Component3() {        System.out.println("Component3");    }}class Root {    Component1 c1 = new Component1();    Component2 c2 = new Component2();    Component3 c3 = new Component3();}public class Stem extends Root {    public static void main(String[] args) {        new Stem();    }}

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10

/** * 派生类自动创建基类的成员变量 * <p/> * Created by wang on 15/8/8. */class Component1 {    public Component1(String s) {        System.out.println("Component1:" + s);    }}class Component2 {    public Component2(String s) {        System.out.println("Component2:" + s);    }}class Component3 {    public Component3(String s) {        System.out.println("Component3:" + s);    }}class Root {    Component1 c1 ;    Component2 c2 ;    Component3 c3 ;    public Root(String s1, String s2, String s3) {        c1 = new Component1(s1);        c2 = new Component2(s2);        c3 = new Component3(s3);    }}public class Stem extends Root {    public Stem(String s1, String s2, String s3) {        super(s1, s2, s3);    }    public static void main(String[] args) {        new Stem("Hello", "Caroline", "Wendy");    }}/** * Output: Component1:Hello Component2:Caroline Component3:Wendy */

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11

/** * 继承 * <p/> * Created by wang on 15/8/7. */class Cleaner {    private String s = "Cleaner";    public static void main(String[] args) {        Cleaner x = new Cleaner();        x.dilute().apply().scrub();        System.out.println(x);    }    public void append(String a) {        s += a;    }    public Cleaner dilute() {        append(" dilute");        return this;    }    public Cleaner apply() {        append(" apply");        return this;    }    public Cleaner scrub() {        append(" scrub");        return this;    }    @Override    public String toString() {        return s;    }}public class Detergent {    private Cleaner c;    public Detergent() {        c = new Cleaner();    }    public static void main(String[] args) {        Detergent d = new Detergent();        d.dilute().apply().scrub();        System.out.println(d);    }    public Detergent dilute() {        c.append(" dilute");        return this;    }    public Detergent apply() {        c.append(" apply");        return this;    }    public Detergent scrub() {        c.append(" Detergent: scrub");        return this;    }    @Override    public String toString() {        return c.toString();    }}/** * Output: Cleaner dilute apply Detergent: scrub */

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12

/** * 确保正确的清理 * <p/> * Created by wang on 15/8/8. */class Component1 {    public Component1(String s) {        System.out.println("Component1:" + s);    }    void dispose() {        System.out.println("Dispose Component1");    }}class Component2 {    public Component2(String s) {        System.out.println("Component2:" + s);    }    void dispose() {        System.out.println("Dispose Component2");    }}class Component3 {    public Component3(String s) {        System.out.println("Component3:" + s);    }    void dispose() {        System.out.println("Dispose Component3");    }}class Root {    Component1 c1 ;    Component2 c2 ;    Component3 c3 ;    public Root(String s1, String s2, String s3) {        c1 = new Component1(s1);        c2 = new Component2(s2);        c3 = new Component3(s3);    }    void dispose() {        c1.dispose();        c2.dispose();        c3.dispose();        System.out.println("Dispose Root");    }}public class Stem extends Root {    public Stem(String s1, String s2, String s3) {        super(s1, s2, s3);    }    @Override    void dispose() {        System.out.println("Dispose Stem");        super.dispose();    }    public static void main(String[] args) {        Stem s = new Stem("Hello", "Caroline", "Wendy");        s.dispose();    }}/** * Output: Component1:Hello Component2:Caroline Component3:Wendy Dispose Stem Dispose Component1 Dispose Component2 Dispose Component3 Dispose Root */

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13

/** * 继承重载 * Created by wang on 15/8/17. */class OneClass {    void sayHello(String s) {        System.out.println(s);    }    void sayHello(int i) {        System.out.println(i + "-Hello");    }    void sayHello(float f) {        System.out.println(f + "~Hello");    }}class Doll {    @Override    public String toString() {        return "Doll";    }}class TwoClass extends OneClass {    public void sayHello(Doll d) {        System.out.println(d + " say Hello");    }}public class OverloadClass {    public static void main(String[] args) {        TwoClass t = new TwoClass();        t.sayHello(new Doll());        t.sayHello("Caroline");        t.sayHello(2);        t.sayHello(0.5f);    }}/** * Output: Doll say Hello Caroline 2-Hello 0.5~Hello */

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14

/** * 使用组合处理对象 * <p/> * Created by wang on 15/8/17. */class Engine {    public void start() {        System.out.println("Start Engine");    }    public void rev() {        System.out.println("Rev Engine");    }    public void stop() {        System.out.println("Stop Engine");    }    public void service() {        System.out.println("Service Engine");    }}class Wheel {    public void inflate(int psi) {        System.out.println("Wheel psi-" + psi);    }}class Window {    public void rollUp() {        System.out.println("Window roll up");    }    public void rollDown() {        System.out.println("Window roll down");    }}class Door {    public Window window = new Window();    public void open() {        System.out.println("Window open");    }    public void close() {        System.out.println("Window close");    }}public class Car {    public Engine engine = new Engine();    public Wheel[] mWheels = new Wheel[4];    public Door left = new Door(), right = new Door();    {        for (int i = 0; i < mWheels.length; ++i) {            mWheels[i] = new Wheel();        }    }    public static void main(String[] args) {        Car c = new Car();        c.engine.start();        c.engine.rev();        c.engine.service();        c.engine.stop();        c.mWheels[1].inflate(20);        c.mWheels[3].inflate(25);        c.left.window.rollUp();        c.right.open();    }}/** * Output: Start Engine Rev Engine Service Engine Stop Engine Wheel psi-20 Wheel psi-25 Window roll up Window open */

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15

package access.local;/** * protected方法类 * Created by wang on 15/8/17. */public class BabaoClass {    protected void drink() {        System.out.println("Babao Drink");    }}

package access.local;/** * protected提供包内访问权限 * Created by wang on 15/8/17. */public class DrinkBabao {    public static void main(String[] args) {        BabaoClass b = new BabaoClass();        b.drink(); // protected提供包内访问权限    }}/** * Output: * Babao Drink */

package access.foreign;import access.local.BabaoClass;/** * 包外访问继承Protected * Created by wang on 15/8/17. */public class LotusBabaoClass extends BabaoClass {    public static void main(String[] args) {        LotusBabaoClass l = new LotusBabaoClass();        l.drink();    }    @Override    protected void drink() {        System.out.print("Lotus ");        super.drink();    }}/** * Output: Lotus Babao Drink */

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16&17

/** * 向上转型 * Created by wang on 15/8/18. */class Amphibian {    public void crawl(){        System.out.println("Amphibian Crawl");    }    protected void color() {        System.out.println("Amphibian Gray");    }}class Frog extends Amphibian {    @Override    protected void color() {        System.out.println("Frog Green");    }}public class UpCastClass {    static public void show(Amphibian a) {        a.crawl();        a.color();    }    public static void main(String[] args) {        Frog frog = new Frog();        show(frog);    }}/** * Output: Amphibian Crawl Frog Green */

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18

/** * final和static final * <p/> * Created by wang on 15/8/18. */class Value {    public int i;    public Value(int i) {        this.i = i;    }    @Override    public String toString() {        return i + "";    }}class Corn {    public static final Value SV = new Value(22);    public final Value fv = new Value(11);}public class FinalTest {    public static void main(String[] args) {        Corn c1 = new Corn();        Corn c2 = new Corn();//        c1.fv = new Value(12); // 静态变量不变        System.out.println(c1.SV.i = 20);        System.out.println(c1.fv.i = 10);        // 静态变量类共享        System.out.println(c1.SV);        System.out.println(c2.fv);    }}/** * Output: 20 10 20 11 */

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19

/** * 空白final * <p/> * Created by wang on 15/8/18. */public class EmptyFinal {    public final int i;    public EmptyFinal() {        i = 12;    }    public EmptyFinal(int i) {        this.i = i;    }    public static void main(String[] args) {        EmptyFinal ef1 = new EmptyFinal();        System.out.println(ef1.i);//        ef.i = 10; // 无法为最终变量 i 指定值        EmptyFinal ef2 = new EmptyFinal(2);        System.out.println(ef2.i);    }}/** * Output: 12 2 */

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20&21

覆盖final方法报错.

/** * 重载 * <p/> * Created by wang on 15/8/20. */class HahaClass {    protected void f() {        System.out.print("HAHA");    }    public final void dummy () {        System.out.println("no voice");    }}class HeheClass extends HahaClass {    @Override    protected void f() {        super.f();        System.out.println(" and HEHE");    }    protected void f(String s) {        System.out.println(s + " say HEHE");    }//    @Override//    public void dummy() {////    }}public class OverrideClass {    public static final void main(String[] args) {        HeheClass h = new HeheClass();        h.f();        h.f("Caroline");    }}/** * Output: (1) HAHA and HEHE Caroline say HEHE (2) 覆盖final方法报错: HeheClass 中的 dummy() 无法覆盖 HahaClass 中的 dummy()；被覆盖的方法为 final */

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22

Error: 无法从最终 one.Insect 进行继承

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23&24

package one;/** * 继承初始化 * <p/> * Created by wang on 15/8/21. */class Insect {    private static int si = numOfLegs("Static si Insect");    protected int j;    private int i = 0;    public Insect() {        // j并未初始化        System.out.println("Insect Constructor: i = " + i + " j = " + j);        j = 10;    }    protected static int numOfLegs(String s) {        System.out.println(s);        return 4;    }}class Beetle extends Insect {    private static int si = numOfLegs("Static si Beetle");    private int i = numOfLegs("Beetle");    // 并未显示调用Insect的构造函数    public Beetle() {        System.out.println("Beetle Constructor: i = " + i + " si = " + si);    }}public class Cockroach extends Beetle {    private static int si = numOfLegs("Static si Cockroach");    private int i = numOfLegs("Cockroach");    // 并未显示调用Insect的构造函数    public Cockroach() {        System.out.println("Cockroach Constructor: i = " + i + " si = " + si);    }    public static void main(String[] args) {        System.out.println("Cockroach Construct");//        Cockroach b = new Cockroach(); // 构造引起静态变量初始化        System.out.println(Cockroach.si); // 调用静态变量    }}/** * Output: (1) 构造初始化 Static si Insect Static si Beetle Static si Cockroach Cockroach Construct Insect Constructor: i = 0 j = 0 Beetle Beetle Constructor: i = 4 si = 4 Cockroach Cockroach Constructor: i = 4 si = 4 (2) 静态变量初始化 Static si Insect Static si Beetle Static si Cockroach Cockroach Construct 4 */