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练习1:(2)创建一个简单的类。第二个类中，将一个引用定义为第一个类的对象。运用惰性初始化来实例化 这个对象。
package test;
public class Manager {
public static void main(String args[]){
Second s=new Second();
s.getFirst();
}
/**
* 打印结果：
*/
}
class First{
}
class Second{
First f;
Second(){
System.out.println("Creating Second");
}
First lazy(){
if(f==null){
System.out.println("Creating First");
f=new First();
}
return f;
}
public First getFirst(){
return lazy();
}
}
练习2：（2）从Detergent中继承产生一个新的类。覆盖scrub()并添加一个名为sterilize()的新方法。
package test;
public class Manager {
public static void main(String args[]){
Sub s=new Sub();
s.apply();s.dilute();s.foam();s.scrub();s.sterilize();
new print(s);
}
/**
* 打印结果：
Cleanser apply() dilute() foam() sub.scrub Detergent.scrub()sub.sterilize()
*/
}
class print{
print(Object obj){
System.out.println(obj);
}
}
class Cleanser{
private String s="Cleanser";
public void append(String a){
s+=a;
}
public void dilute(){
append(" dilute()");
}
public void apply(){
append(" apply()");
}
public void scrub(){
append(" scrub() ");
}
public String toString(){
return s;
}
public static void main(String[] args){
Cleanser x=new Cleanser();
x.dilute();x.apply();x.scrub();
new print(x);
}
}
class Detergent extends Cleanser{
public void scrub(){
append(" Detergent.scrub()");
}
public void foam(){
append(" foam()");
}
}
class Sub extends Detergent{
public void scrub(){
append(" sub.scrub");
super.scrub();
}
public void sterilize(){
append("sub.sterilize()");
}
}
练习3（2)证明前面两句话（即使你不为Cartoon创建构造器，编译器也为会你合成一个默认的构造器，该构造器将调用基类的构造器）
package test;
public class Manager {
public static void main(String args[]){
new Cartoon();
}
/**
* 打印结果：
Art constructor
Drawing constructor
*/
}
class print{
print(Object obj){
System.out.println(obj);
}
}
class Art{
Art(){
new print("Art constructor ");
}
}
class Drawing extends Art{
Drawing(){
new print("Drawing constructor ");
}
}
class Cartoon extends Drawing{
}
练习4（2）证明基类构造器总是会被调用，在导出类构造器之前被调用。
package test;
public class Manager {
public static void main(String args[]){
new Child();
}
/**
* 打印结果：
父类构造器输出
子类构造器输出
*/
}
class print{
print(Object obj){
System.out.println(obj);
}
}
class Parent{
Parent(){
new print("基类构造器输出");
}
}
class Child extends Parent{
Child(){
new print("子类构造器输出");
}
}
练习5：（1）创建两个带有默认构造器（空参数列表）的类A和类B。从A中继承产生一个名为C的新，并在C内创建一个B类的成员。不要给C编写构造器。创建一个C类的对象并观察其结果。
package test;
public class Manager {
public static void main(String args[]){
new C();
}
/**
* 打印结果：
A()……
B()……
B()……
C()……
*/
}
class print{
print(Object obj){
System.out.println(obj);
}
}
class A{
A(){
new print("A()……");
}
}
class B{
B(){
new print("B()……");
}
}
class C extends A{
private B b=new B();
C(){
new print("C()……");
}
private B b2=new B();
}
练习6：（1）用Chess证明前面两名话
package test;
public class Manager {
public static void main(String args[]){
new Chess();
}
/**
* 打印结果：
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
Implicit super constructor BordGame() is undefined. Must explicitly invoke another constructor
at test.Chess.(Manager.java:32)
at test.Manager.main(Manager.java:6)
*/
}
class print{
print(Object obj){
System.out.println(obj);
}
}
class Game{
Game(int i){
new print("Game constructor");
}
}
class BordGame extends Game{
BordGame(int i){
super(i);
new print("BordGame constructor");
}
}
class Chess extends BordGame{
Chess(){//Implicit super constructor BordGame() is undefined. Must explicitly invoke another constructor
new print("Chess constructor");
}
}
练习7：（1）修改练习5，使A和B以带参数的构造器取代默认的构造器。为C写一个构造器，并在其中执行所有初始化。
package test;
public class Manager {
public static void main(String args[]){
new C();
}
/**
* 打印结果：
A()……
B()……
B()……
C()……
*/
}
class print{
print(Object obj){
System.out.println(obj);
}
}
class A{
A(int i){
new print("A()……");
}
}
class B{
B(){
new print("B()……");
}
}
class C extends A{
private B b=new B();
C(){
super(1);//必须
new print("C()……");
}
private B b2=new B();
}
练习8：（1）创建一个基类，它仅有一个非默认构造器；再创建一个导出类，它带有默认构造器和非默认构造器。在导出类的构造器中调用基类的构造器。
package test;
public class Test {
public static void main(String[] args) {
}
}
class A{
/** 非默认构造器 **/
A(int i){
System.out.println("基类");
}
}
class B extends A{
B(){
super(1);/** 调用基类构造函数 **/
}
B(int i){
super(i);/** 调用基类构造函数 **/
System.out.println("导出类");
}
}
练习9：（2）创建一个Root类，令其含有名为Component1、Component 2、Component3的类的各一个实例（这些也由你写）。从Root中派生一个类Stem，也含有上述各“组成部分”。所有的类都应带有可打印出类的相关信息的默认构造器。
package test;
public class Test {
public static void main(String[] args) {
new Stem();
}
/**
* 输出
Component1 constructor
Component2 constructor
Component3 constructor
Root constructor
Component1 constructor
Component2 constructor
Component3 constructor
Stem constructor
*/
}
class Root{
private Component1 component1=new Component1();
private Component2 component2=new Component2();
private Component3 component3=new Component3();
Root(){
System.out.println("Root constructor");
}
}
class Stem extends Root{
private Component1 component1=new Component1();
private Component2 component2=new Component2();
private Component3 component3=new Component3();
Stem(){
System.out.println("Stem constructor");
}
}
class Component1{
Component1(){
System.out.println("Component1 constructor");
}
}
class Component2{
Component2(){
System.out.println("Component2 constructor");
}
}
class Component3{
Component3(){
System.out.println("Component3 constructor");
}
}
练习10：（1）修改练习9，使每个类都仅具有非默认的构造器。
package test;
public class Test {
public static void main(String[] args) {
new Stem(1);
}
/**
* 输出
Component1 constructor 1
Component2 constructor 2
Component3 constructor 3
Root constructor
Component1 constructor 1
Component2 constructor 2
Component3 constructor 3
Stem constructor
*/
}
class Root{
private Component1 component1=new Component1(1);
private Component2 component2=new Component2(2);
private Component3 component3=new Component3(3);
Root(int i){
System.out.println("Root constructor");
}
}
class Stem extends Root{
private Component1 component1=new Component1(1);
private Component2 component2=new Component2(2);
private Component3 component3=new Component3(3);
Stem(int i){
super(i);
System.out.println("Stem constructor");
}
}
class Component1{
Component1(int i){
System.out.println("Component1 constructor "+i);
}
}
class Component2{
Component2(int i){
System.out.println("Component2 constructor "+i);
}
}
class Component3{
Component3(int i){
System.out.println("Component3 constructor"+i);
}
}
练习11：（3）修改Detergent.java。让它使用代理。
package test;
public class Test {
public static void main(String args[]){
Sub s=new Sub();
s.apply();s.dilute();s.foam();s.scrub();s.sterilize();
new print(s);
}
/**
* 打印结果：
Cleanser apply() dilute() foam() sub.scrub Detergent.scrub()sub.sterilize()
*/
}
class print{
print(Object obj){
System.out.println(obj);
}
}
class Cleanser{
private String s="Cleanser";
public void append(String a){
s+=a;
}
public void dilute(){
append(" dilute()");
}
public void apply(){
append(" apply()");
}
public void scrub(){
append(" scrub() ");
}
public String toString(){
return s;
}
public static void main(String[] args){
Cleanser x=new Cleanser();
x.dilute();x.apply();x.scrub();
new print(x);
}
}
class Detergent{
Cleanser Cleanser=new Cleanser();
public void append(String str){
Cleanser.append(str);
}
public void dilute(){
append(" dilute()");
}
public void apply(){
append(" apply()");
}
public String toString(){
return Cleanser.toString();
}
public void scrub(){
append(" Detergent.scrub()");
}
public void foam(){
append(" foam()");
}
}
class Sub extends Detergent{
public void scrub(){
append(" sub.scrub");
super.scrub();
}
public void sterilize(){
append("sub.sterilize()");
}
}
练习12：（3）将一个适当的dispose()方法的层次结构添加到练习9的所有类中。
package test;
public class Test {
public static void main(String[] args) {
Stem s=new Stem();
try{
s.toString();
}finally{
s.dispose();
}
}
/**
* 输出
Component1 constructor
Component2 constructor
Component3 constructor
Root constructor
Component1 constructor
Component2 constructor
Component3 constructor
Stem constructor
Stem dispose
Root dispose
*/
}
class Root{
private Component1 component1=new Component1();
private Component2 component2=new Component2();
private Component3 component3=new Component3();
Root(){
System.out.println("Root constructor");
}
void dispose(){
System.out.println("Root dispose");
}
}
class Stem extends Root{
private Component1 component1=new Component1();
private Component2 component2=new Component2();
private Component3 component3=new Component3();
Stem(){
System.out.println("Stem constructor");
}
void dispose(){
System.out.println("Stem dispose");
super.dispose();
}
}
class Component1{
Component1(){
System.out.println("Component1 constructor");
}
void dispose(){
System.out.println("Component1 dispose");
}
}
class Component2{
Component2(){
System.out.println("Component2 constructor");
}
void dispose(){
System.out.println("Component2 dispose");
}
}
class Component3{
Component3(){
System.out.println("Component3 constructor");
}
void dispose(){
System.out.println("Component3 dispose");
}
}
练习13：（2）创建一个类，它应带有一个被重载了三次的方法。继承产生一个新类，并添加一个该方法的新的重载定义，展示这四个方法在导出类中都是可以使用的。
package test;
public class Test {
public static void main(String[] args) {
Stem s=new Stem();
s.a();
int i=10;
s.a(i);
float f=10f;
s.a(f);
double d=10d;
s.a(d);
}
/**
* 输出
a()
a(int)10
a(float)10.0
a(double)10.0
*/
}
class Root{
void a(){
System.out.println("a()");
}
void a(int i){
System.out.println("a(int)"+ i);
}
void a(float i){
System.out.println("a(float)"+ i);
}
}
class Stem extends Root{
void a(double i){
System.out.println("a(double)"+ i);
}
}
练习14：（1）在Car.java中给Engine添加一个service(),并在main()中调用该方法。
