我看完了Java类,与C++相比，复杂了一点。其中有类的嵌套定义即内部类，枚举类等。
我看这两节花了我很多时间。其中有一些概念还是有点难懂。
下面，我详细总结内部类与枚举类。
内部类
内部类的主要作用：
- 提供更好的封装。
- 内部类成员可以直接访问外部类的私有数据。进而可以实现回调
- 匿名内部类适合用于创建那些仅需要一次使用的类。
注意，匿名内部类，在枚举中使用十分适合，应用广泛。
1.1非静态内部类
1.2静态内部类
1.3使用内部类
1.4匿名内部类
1.5闭包与回调
因为内部类作为其外部类的成员，所以可以使用public private protected default
public class Cow { private double weight; public Cow(){} public Cow(double weight) { this.weight=weight; } private class CowLeg { private double length; private String color; public CowLeg(){} public CowLeg(double length,String color) { this.length=length; this.color=color; }
public void setLength(double length) { this.length=length; } public void setColor(String color) { this.color=color; } public double getLength() { return this.length; } public String getColor() { return this.color; }
public void info() { System.out.println("当前的长方形颜色是：" +color+",高:"+length); System.out.println("长方形的重量是："+ weight); } } public void test() { CowLeg c1=new CowLeg(1.12,"黑白相间"); c1.info(); } public static void main(String[] args) { // TODO Auto-generated method stub Cow cow =new Cow(378.9); cow.test(); } } |
可以看到内部类与外部类的区别了吧！！
在非静态内部类里可以直接访问外部类的private成员，这是因为在非静态内部类对象里，保存了一个它寄存的外部类的对象的引用。
简单点説：必须有一个非静态内部类实例必须寄存在外部类实例里,因此，在外部类中不能使用内部类中的成员变量
System.out.println(new Cow().weight);
如果外部类成员变量、内部类成员变量与内部类里方法的局部变量同名，则可以通过:
public class StaticInnerClassTest {
private int propl=5; private Object StaticInnerClass; private static int prop2=9; public static void info() { System.out.println("我是静态变量"); } static class StaticInnerClass { private static int age; public void accessOuterPro() { System.out.println(prop2); info(); } } public static void main(String[] args) { // TODO Auto-generated method stub StaticInnerClassTest test=new StaticInnerClassTest(); StaticInnerClassTest.StaticInnerClass demo=new StaticInnerClassTest.StaticInnerClass(); demo.accessOuterPro(); }
} |
这个类属于外部类的本身，称类内部类，并且 static不可以修饰外部类，但可以修饰内部类.
public class CreateInnerLnstance {
class In { public In(String msg) { System.out.println(msg); } } public static class CreateInnerInstance { public static void testt() {@SuppressWarnings("unused") CreateInnerLnstance.In in = new CreateInnerLnstance().new In("信息测试");}
} @SuppressWarnings("static-access") public static void main(String[] args) { // TODO Auto-generated method stub CreateInnerLnstance.CreateInnerInstance in = new CreateInnerLnstance.CreateInnerInstance(); in.testt(); }
} |
package test;
public class tes {
public static class t { public t() { System.out.println("I am outclass"); } public static class t1 { public t1() { System.out.println("I am inner1"); } public static class t2 { public t2() { System.out.println("I am inner2"); } } } } public static void main(String[] args) { // TODO Auto-generated method stub tes.t.t1.t2 testt2=new tes.t.t1.t2(); } } |
OuterClass.new InnerConstructor ()
非静态内部类的构造器必须使用外部类对象来调用。因此在使用上一句时，必须已经创建了外部类了。
class Out { class In { public In(String msg) { System.out.println(msg); } } } class SubClass extends Out.In { public SubClass(Out out)//此参数不可少！！！！ { out.super("hello");//此句话不可少！！！！ /*** 函意是:调用out的内部类的构造函数 ***/
} } |
new OuterClass.InnerConstructor ()
package Anonymous; interface Product { public double getPrice(); public String getName(); } public class AnonyMousTest {
public void test(Product p) { System.out.println("购买了一个"+p.getName()+" 价格是 "+p.getPrice()); } public static void main(String[] args) { // TODO Auto-generated method stub AnonyMousTest ta = new AnonyMousTest(); ta.test( new Product() { public double getPrice() { return 1; } public String getName() { return "AGP显卡"; } } ); }
} |
package AnonymousInner; abstract class Device { private String name; public abstract double getPrice(); public Device(){} public Device(String name) { this.name = name; } public String getName() { return this.name; } } public class AnonymousInner { public void test(Device d) { System.out.println("购买了一个"+d.getName()+",花掉了"+d.getPrice()); } public static void main(String[] args) { // TODO Auto-generated method stub AnonymousInner ai = new AnonymousInner(); ai.test(new Device("电子示波器") { public double getPrice() { return 67.8; } }); Device d = new Device() { { System.out.println("匿名内部类的初始化块..."); } public double getPrice() { return 56.2; } public String getName() { return "键盘"; } }; ai.test(d); }
} |
interface A { void test(); } public class Atest {
public static void main(String[] args) { // TODO Auto-generated method stub final int age = 1000; A a =new A() { public void test() { System.out.println(age); } }; a.test(); }
}
|
回调：某个方法一旦获得了内部类对象的引用后，就可以在适合的时候反过来云调用外部类实例的方法。
interface Teachable { void work(); } class Programmer {
private String name; public Programmer(){} public Programmer(String name) { this.name=name; } public String getName() { return name; } public void work() { System.out.println(name+"在灯下认真敲键盘。。。"); } } class TeachableProgrammer extends Programmer { public TeachableProgrammer(){} public TeachableProgrammer(String name) { super(name); } private void teach() { System.out.println(getName()+"老师在讲台上讲解。。。"); } private class Closure implements Teachable { public void work() { teach(); } } public Teachable getCallbackReference() { return new Closure(); } } public class ATest { public static void main(String[] args) { TeachableProgrammer tp = new TeachableProgrammer("李刚"); tp.work(); tp.getCallbackReference().work();
}
} |
public class EnumTest {
public void judge(SeasonEnum s) { switch(s) { case SPRING: System.out.println("春暖花开，正好踏青"); break; case SUMMER: System.out.println("夏日炎炎，适合游泳"); break; case FALL: System.out.println("秋高气爽，进补及时"); break; case WINTER: System.out.println("冬日雪飘，围炉赏雪"); break; } } public static void main(String[] args) { // TODO Auto-generated method stub for(SeasonEnum s:SeasonEnum.values()) { System.out.println(s); } new EnumTest().judge(SeasonEnum.SPRING); }
} |
public enum SeasonEnum { SPRING,SUMMER,FALL,WINTER; } |
public enum Gender { MALE("man"),FEMALE("woman"); private final String name; private Gender(String name) { this.name=name; } public String getName() { return this.name; } } |
public class GenderTest {
/** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub Gender g= Enum.valueOf(Gender.class, "FEMALE"); System.out.println(g+" stand for "+g.getName()); }
} |