接口Interface)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.接口的所有方法默认都是public,abstract和non-static�br /> 2.接口的所有变量默认都是public,static,final�所�接口的变量不能改�在它的实现类�
3.接口的实现类实现的方法必™åÕd’ŒæŽ¥å£çš„方法抛出同æ ïLš„异常,不许是子¾c?˜q™å’Œoverride不一æ ?同样,如果接口æ–ÒŽ³•æ²¡æœ‰æŠ?实现æ–ÒŽ³•ä¹Ÿä¸èƒ½æŠ›.
4.实现¾cÕd®žçŽ°çš„æ–ÒŽ³•å¿…须昑ּçš„声明成public,什么都不写都不è¡?å•?!!
5.接口不能声明成final,要不它怎么被实现呢(˜q™å¥½åƒåˆæ˜¯åºŸè¯å•Š
6.一个类实现两个接口,如果两个接口有相同的æ–ÒŽ³•,实现¾cÕd°±å®žçŽ°˜q™ä¸ªæ–ÒŽ³•,没问题的.

内嵌¾c»Inner Class)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.内嵌¾cÕd¯ä»¥è®¿é—®outer¾cȝš„ä»ÖM½•å˜é‡,包括¿Uæœ‰çš?
2.静态inner¾c?只能讉K—®outer¾cȝš„ä»ÖM½•static变量
2.1内嵌¾cÕd¯ä»¥æ˜¯final,abstractçš?br /> 3.我靠,æ–ÒŽ³•å†…的内嵌¾cÖM¸èƒ½äØ“static: void test(){ static class A{}} XXXXX!!!!
4.我靠,æ–ÒŽ³•å†…的内嵌¾cÖM¹Ÿä¸èƒ½å¸¦ä“Q何modifier,void test(){ public class A{}} XXXXX!!!!
5.我靠,æ–ÒŽ³•å†…的内嵌¾cÕdªèƒ½è®¿é—®æ–¹æ³•å†…çš„final变量,但是,可以讉K—®outer¾cȝš„ä»ÖM½•å˜é‡.
6.匿名¾cÖM¸èƒ½æœ‰æž„造器,但声明时候带参数,相当于构造器的参æ•îC¼ é€?
class ABC{}
class ABCD{private ABCD(int i){}}
ABC test3(){return new ABC(){};}
ABCD test4(){return new ABCD(3){};}
interface iii{}
iii test5(){return new iii(){};}
//class BCD extends ABCD{} compile error,å› äØ“,
看上面就知道,new iii(){};实际上匿名类实现了iii接口;new ABC(){};实际上是匿名¾cȝ‘ô承了ABC.
8.
class A {private A(){System.out.println("a!");}}
class B extends A{}
我靠,没错!B实例的时候会ä¸ÕdŠ¨è°ƒç”¨çˆ¶ç±»Açš„æž„é€?即ä‹É是privateçš?看来也没问题!!!
9.内部¾cÕd¯ä»¥æœ‰synchronizedæ–ÒŽ³•,那么锁是˜q™ä¸ªå†…部¾c?跟外部类没一点关¾p?内外分别çš?在锁的问题上.
10.外部¾cÖM¸èƒ½é€šè¿‡this被访é—?this˜q™æ—¶å€™åº”该指的是内部¾c?享用外部¾cȝš„成员ž®Þq›´æŽ¥ç”¨,不用加ä“Q何限定词
11.如何用this呢请�
class Outer{ int i;
class Inner{
class InnerInner{
void Test(){
Outer.this.i=1;
}
}
}
}
看见了吧,¾cÕd.this.变量å?可以引用到i,½W¬ä¸€‹Æ¡çœ‹åˆ°å§,嘿嘿,孤陋寡闻.
12.注意˜q™ä¸¤¿Uå†™æ³•éƒ½å¯ä»¥
Class Outer.Inner i = new Outer().new Inner();
或� Class o= new Outer(); Class Outer.Inner i=o.new Inner();

¾U¿ç¨‹Thread)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
åŽÈœ‹Threadçš„API!!!!
1.¾U¿ç¨‹å¯åŠ¨å¿…须通过start函数.
2.run函数不许也只能是public�
3.¾U¿ç¨‹æœ‰ä¼˜å…ˆçñ”ä»?åˆ?0,通过Thread.setPriority(int);来改å?不能­‘…过10,否则会出现运行异å¸?br /> 4.¾U¿ç¨‹ä¼˜å…ˆ¾U§é»˜è®¤æ˜¯5,即NORM_PRIORITY.NORM_PRIORITY是Thread的静态变量吗
5.Thread.yeild();是静态方æ³?所ä»?使用格式是Thread.yield();她强˜q«å½“前的˜q›ç¨‹æ”‘Ö¼ƒCUP.
6.sleep(1000),是说¾U¿ç¨‹ç¡è§‰1¿U?然后,˜q›å…¥Ready状æ€?注意,不是˜qè¡ŒçŠ¶æ€?它还要等OS来调度来获得CUP.

java.lang.*;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.数组的科� int ia[][]={{1,2},null}; int ib[][]=(int[][])ia.clone();
2.什么是NaN然后看ceil(NaN),floor(NaN),...
3.Math.floor(-1.1f);//-2.0
Math.ceil(-1.1f);//-1.0
Math.round(-1.6d)//-2
4.0=<1
5.Math,Interger,Boolean...½{‰ç±»åž‹åŒ…装类都是finalçš?不可¾l§æ‰¿
6.int round(float); long round(double);å”?round永远˜q”回不了ž®æ•°ç‚?br /> 7.static double ceil(double)
8.static double floor(double)注意åQŒceil,floor的只有这个double版本,什么都转成double!
9.static double sin(double 弧度); ˜q˜æœ‰cos,tan
10. new String; 可以是byte[];char[];String;StringBuffer
11. String的一些函� int length(); char charAt(int); String toUpperCase(); String toLowerCase();
12. String("Abc").equals(String("abc"))不相½{‰çš„,不然ž®×ƒ¸ä¼šæœ‰boolean equalsIgnoreCase(String)函数
13."012345678"是一个串的顺序号ç ?indexOf('1'),indexOf("1")都返å›?,subString(1,5)æ˜?345,嘿嘿:æ˜?[)"çš„æ„Ÿè§?br /> 14, trim()˜qžtab都退æ¯?"\t\n java ",trim()一下就只剩ä¸?java"äº?br /> 15. 关于对象的科éš?åŽÕd–³å–³API
16. "abcd".trim(),"abcd" + new String("ef")都是合理的写æ³?br /> 17. StringBufferçš?个构造器: ()初始化容量äØ“16,(int 初始化容é‡?,(String),初始化容量äؓ串长加上16
18. StringBuffer的一些函� String toString(); append();reverse();insert();delete(int start,int end);deleteCharAt(int);setLength(int newLength);
19. String s=""; StringBuffer sb=new StringBuffer(); if (s==sb){}¾~–译é”?å› äØ“,s,sb¾cÕdž‹ä¸ä¸€æ ?不能比较
集合:
1.各接口和¾cȝš„关系,只有最后一个是¾c?br /> Collection:List:vector,ArrayList,LinkedList
Map:SortedMap:TreeMap
Collection:Set:SortedSet:TreeSet
Map:HashTable
Collection:Set:HashSet

基础Base)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.java applicationçš„main可以不是publicçš?但必™åÀL˜¯staticçš?br /> 2.一个文件只能有一个public¾c?而且˜q˜å¾—跟文件名一æ ?包括大小å†?br /> 3.变量只能是字æ¯?$,_å¼€å¤?接下来的½W¬äºŒä¸ªå¯ä»¥æ˜¯,æ•°å­—
4.ch\u0061r='a'; char \u0063='b'; char c='\u0063';都是合法çš?br /> 5.1e-5d,合法.e-5d不合æ³?必须有前面的¾pÀL•°
6.int[] i[]={null{1,2}}正确! int i[]={1,2,3,} 正确!","和没有的效果一æ ?br /> 7.局部array,跟变量一æ ?使用前要初始åŒ?br /> 8.mainæ–ÒŽ³•å¯ä»¥ä¸ºfinal

操作½W¦å’Œåˆ†é…½W?Operator and Assignment)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.System.out.printl(1+2+"3");//33 System.out.printl("1"+2+3);//123
2.int i=0; i=i++;i=i++;i=i++; ¾l“æžœ,i=0!
3.int i[]; index=0; i[index]=index=5; ¾l“æžœæ˜?i[0]=5;!!!
4.byte b=10;可以,å› äØ“,10可以被自动从int转成byte
5.接下æ?byte b=b+10;不可ä»?!å› äØ“,10+b后的int无法被自动从int转成byte,问我,我也不知道äؓ什ä¹?é?
6.byte b1 = 4; byte b2 = 6; b1 = b1 + b2;é”?¾~–译é”?b1 + b2å?必须强制转成byte,b1x1+b2);
7.XOR 一æ ïLš„ä¸?åQŒä¸ä¸€æ ·äØ“1 1,1=0;0,0=0;1,0/0,1=1
8. x == Float.NaN¾~–译错，应该是Float.IsNaN
9. x == Double.POSITIVE_INFINITY¾~–译可以
10.-1æ˜?111.... 1111,<<永远双™¡¥é›Óž¼Œ>>正补é›Óž¼Œè´Ÿè¡¥ä¸€åQ?gt;>>恒补é›?br /> 10.1 -1>>多少位都æ˜?1 ; 1<<31变成了最ž®è´Ÿæ•?1000....0000
11.最大正数是01111....1111
12.最ž®è´Ÿæ•°æ˜¯1000....0000(-2147483648)
13. a instanceof b,b必须是类/接口åQŒä¸èƒ½æ˜¯å®žä¾‹
--------补充------------------------------
1. byte,short,char 都存åœ?var = -var;¾~–译错误,å› äØ“,˜q™æ—¶å€™çš„-var已经自动转成个int¾cÕdž‹äº?br /> 2. int/0会扔出ArithmeticException
double,float/0得INF或�INF
0/0å¾—NaN
3. int a-b-c;是不½W¦åˆå‘½åè§„则的变量名¾~–译会出é”?
4. char a='\u0001';å¯? char b=\u0001;¾~–译é”?
5. boolean b1,b2,b3,b4,b5;
b1 = b2==b3;
b1 = b2<=b3 && b4==b5;
b1 = b2==b3==true
都是对的!�变�
b1 = b2==b3==b4 XXXXXXX¾~–译é”?
6. 1>>1 �
7. %= <<= =>> =>>>都是合法½W¦å·
8. --1-10*4 ˜q™ç§å†™æ³•æ²¡é”™,ž®±æ˜¯ (--1)-10*4
9. k=1;++k + k++ + +k ;¾l“æžœæ˜?,相当äº?(++2)+(2++)+(+3)
10.标号不能标示声明.
hi:
if {
break hi;
//break hi1;不行,不能向后调è{
}
//hi1:不行,不能攑֜¨å£°æ˜Žå‰?br /> int i;
hi1:
i=1;
11.public static void main(String s[]) throws Exception{}可以�main可以扔出异常
12. hi:
if(b==true){break hi;}
break 标号åQŒå¯ä»¥ç”¨åœ¨if里面.别的ä»ÖM½•éƒ½ä¸è¡?包括break,continue 标号.
13.int x = i*-j; 我靠,没问题的!!!¾~–译没错! int x = i*j++ + +i++; ˜q™ä¸ªä¹Ÿæ²¡é—®é¢˜,

变量修饰½W?Modifier)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.最外面一层的¾cÖM¸èƒ½å£°æ˜Žæˆprotectå’Œpraviteçš?br /> 2.同一个类的两个实例之间可以访问彼此的¿Uæœ‰æ–ÒŽ³•å’Œç§æœ‰å˜é‡?é…?br /> 3.protect和无修饰½W¦çš„具体区别关于外包可以讉K—®è¢«å­¾c»è®¿é—®çš„是哪ä¸?br /> 4.成员变量被修饰成finalå?必须声明时候就赋初值或者在构造器里面赋初å€?别指望她可以得到defaultå€?
5.抽象æ–ÒŽ³•ä¸èƒ½æ˜¯staticçš?!!
6.静态方法将随着¾cȝš„变化而变åŒ?看例å­?
class Parent{
static void test(){System.out.println("hi,parent")};
}
class Child extends Parent{
static void test(){System.out.println("hi,child")};
}
Parent p = new Child();
p.test(); //打出来的是hi,parent!
7.静态方法可以通过¾cȝš„实例调用.
new Child().test(); �Child.test(); 都OK!
8.transient只能用在¾cȝš„成员变量ä¸?不能用在æ–ÒŽ³•é‡?
9.transient变量不能是finalå’Œstaticçš?br /> 10.nativeæ–ÒŽ³•å¯ä»¥æ˜¯private,abstractdçš?/p>

‹¹ç¨‹æŽ§åˆ¶
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1。不可到辄¡š„语句声明为错åQšwhile(false){} ;for(;false{};if(false){}都无法编è¯?br /> 2。for(½W¬ä¸€éƒ¨åˆ†;的第一部分可以用来声明或者赋å€û|¼Œä½†ä¸èƒ½ä¸¤è€…都
3。byte b; switch  { case 200: // 200 not in range of byteåQŒå› ä¸?00­‘…过b的范å›ß_¼Œž®†ç¼–译错è¯?br /> 4。带标签的continue回达到标½{„¡š„位置åQŒä»Žæ–°è¿›å…¥ç´§æŽ¥åœ¨æ ‡ç­¾åŽé¢çš„åó@çŽ?br /> 5。带标签的break会中断当前åó@环，òq¶è{¿UÕdˆ°æ ‡ç­¾æ ‡ç¤ºçš„的循环的末ž®?/p>

转型和上�Converting and Casting)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Binary operators convert the smaller(less precise) operand to the type of the larger(more precise) operand.
All operators will convert things smaller than ints to ints or larger. This includes char 's!
1.byte,char,short默认转成int
2.byte->short->int->long->float->double
char^
˜q™æ˜¯é»˜è®¤å¯ä»¥è½¬åž‹çš„æ–¹å?反了必须要显式cast! 特别注意:long->float是默认的,别看long64,float32,嘿嘿
˜q˜æœ‰ž®±æ˜¯çœ‹å¾—出来,charå’?byte,short之间无法互相默认转换
3.float f=1/3; OK!float f=1.0/3.0;¾~–译出错,å› äØ“1.0/3.0¾l“果是doubleçš?噢噢~,错喽!!
4.int i=1; byte b=i;�需要显式cast.
final i=1; byte b=i;ž®±ok! 我也不知道äؓ什ä¹?finalž®±å¯ä»?而且,据我实验只有intå’Œbyteçš„å…³¾p»è¿™æ ?其他不行.
5.int i[]; Object[] obj=i;� Object obj=i;� 数组只能转成Object,而不能是Object[]
6.int i[]; Object[] obj;i=(int[])obj; å¯? 对象可以通过昑ּæ¥è{成一个数¾l?

I/O
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.File¾cȝš„一些重要方æ³?isFile();isDirectory();String[] list();exists();getAbsolutePath();getParent();
2.通过delete();mkdir();rename(File newname);可以操纵文äšg,但是却改变不了文件的内容
2.1 File¾cÀL— æ³•æ”¹å˜å½“前目å½?除非重新创徏一个File对象.
3.InputStreamReader(InputStream in,String encodingName);
OutputStreamReader(OutputStream in,String encodingName);
Encoding: 8859_1是Latin-1,包含ASCII
4.关闭close一个流,ž®Þp‡ªåŠ¨è°ƒç”¨äº†flush.
5.System.in,System.out,System.err,由JVM自动创徏
6.RandomAccessFile(File file,String mode);mode�r,rw

• 知道如何在特定的条äšg下选择适合的集合类/接口ã€?
• 能正¼‹®åœ°å®žçŽ°hashcodeæ–ÒŽ³•ã€?

½W¬ä¸€èŠ?nbsp;         所有接口和class定义

1:Set

public interface Set extends Collection

A collection that contains no duplicate elements. More formally, sets contain no pair of elements e1 and e2 such that e1.equals(e2), and at most one null element. As implied by its name, this interface models the mathematical set abstraction.

2:SortedSet

public interface SortedSet extends Set.

A set that further guarantees that its iterator will traverse the set in ascending element order, sorted according to the natural ordering of its elements (see Comparable), or by a Comparator provided at sorted set creation time.

3:HashSet

public class HashSet extends AbstractSet implements Set, Cloneable, Serializable

This class implements the Set interface, backed by a hash table (actually a HashMap instance). It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time. This class permits the null element.

4:TreeSet

public class TreeSet extends AbstractSet implements SortedSet, Cloneable, Serializable

This class implements the Set interface, backed by a TreeMap instance. This class guarantees that the sorted set will be in ascending element order, sorted according to the natural order of the elements (see Comparable), or by the comparator provided at set creation time, depending on which constructor is used.

5:LinkedHashSet:

public class LinkedHashSet extends HashSet implements Set, Cloneable, Serializable

Hash table and linked list implementation of the Set interface, with predictable iteration order. This implementation differs from HashSet in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is the order in which elements were inserted into the set (insertion-order). Note that insertion order is not affected if an element is re-inserted into the set. (An element e is reinserted into a set s if s.add(e) is invoked when s.contains(e) would return true immediately prior to the invocation.)

5:Map

public interface Map

An object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most one value.

6:SortedMap

public interface SortedMap extends Map

A map that further guarantees that it will be in ascending key order, sorted according to the natural ordering of its keys (see the Comparable interface), or by a comparator provided at sorted map creation time. (This interface is the map analogue of the SortedSet interface.)

7:HashMap(允许key和value为NULL)

public class HashMap extends AbstractMap implements Map, Cloneable, Serializable

Hash table based implementation of the Map interface. This implementation provides all of the optional map operations, and permits null values and the null key. (The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls.) This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time

8:TreeMap

public class TreeMap extends AbstractMap implements SortedMap, Cloneable, Serializable

Red-Black tree based implementation of the SortedMap interface. This class guarantees that the map will be in ascending key order, sorted according to the natural order for the key's class (see Comparable), or by the comparator provided at creation time, depending on which constructor is used.

9:HashTable(不允许key和value为NULL)

public class Hashtable extends Dictionary implements Map, Cloneable, Serializable.

This class implements a hashtable, which maps keys to values. Any non-null object can be used as a key or as a value.

9:LinkedHashMap

public class LinkedHashMap extends HashMap

Hash table and linked list implementation of the Map interface, with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order). Note that insertion order is not affected if a key is re-inserted into the map. (A key k is reinserted into a map m if m.put(k, v) is invoked when m.containsKey(k) would return true immediately prior to the invocation.)

9:IdentityHashMap

public class IdentityHashMap extends AbstractMap implements Map, Serializable, Cloneable

This class implements the Map interface with a hash table, using reference-equality in place of object-equality when comparing keys (and values). In other words, in an IdentityHashMap, two keys k1 and k2 are considered equal if and only if (k1==k2). (In normal Map implementations (like HashMap) two keys k1 and k2 are considered equal if and only if (k1==null ? k2==null : k1.equals(k2)).)

This class is not a general-purpose Map implementation! While this class implements the Map interface, it intentionally violates Map's general contract, which mandates the use of the equals method when comparing objects. This class is designed for use only in the rare cases wherein reference-equality semantics are required.

10:List

public interface List extends Collection

An ordered collection (also known as a sequence). The user of this interface has precise control over where in the list each element is inserted. The user can access elements by their integer index (position in the list), and search for elements in the list.

Unlike sets, lists typically allow duplicate elements. More formally, lists typically allow pairs of elements e1 and e2 such that e1.equals(e2), and they typically allow multiple null elements if they allow null elements at all.

11:ArrayList

public class ArrayList extends AbstractList implements List, Cloneable, Serializable

Resizable-array implementation of the List interface. Implements all optional list operations, and permits all elements, including null. In addition to implementing the List interface, this class provides methods to manipulate the size of the array that is used internally to store the list. (This class is roughly equivalent to Vector, except that it is unsynchronized.)

12:LinkedList

public class LinkedList extends AbstractSequentialList implements List, Cloneable, Serializable

Linked list implementation of the List interface. Implements all optional list operations, and permits all elements (including null). In addition to implementing the List interface, the LinkedList class provides uniformly named methods to get, remove and insert an element at the beginning and end of the list. These operations allow linked lists to be used as a stack, queue, or double-ended queue (deque).

13:Vector

public class Vector extends AbstractList implements List, Cloneable, Serializable

The Vector class implements a growable array of objects. Like an array, it contains components that can be accessed using an integer index. However, the size of a Vector can grow or shrink as needed to accommodate adding and removing items after the Vector has been created.

14:Collection

public interface Collection

The root interface in the collection hierarchy. A collection represents a group of objects, known as its elements. Some collections allow duplicate elements and others do not. Some are ordered and others unordered. The SDK does not provide any direct implementations of this interface: it provides implementations of more specific subinterfaces like Set and List. This interface is typically used to pass collections around and manipulate them where maximum generality is desired.

15:Collections

public class Collections extends Object

This class consists exclusively of static methods that operate on or return collections. It contains polymorphic algorithms that operate on collections, "wrappers", which return a new collection backed by a specified collection, and a few other odds and ends.

• 能正¼‹®å£°æ˜ŽåŒ…、import、类åQˆåŒ…括内部类åQ‰ã€æŽ¥å£ã€æ–¹æ³•ï¼ˆåŒ…括用于开始一个类的执行的mainæ–ÒŽ³•åQ‰ã€å˜é‡ï¼Œòq¶æ­£¼‹®ä‹É用修饰符ã€?
• 能够正确使用实现了接口的¾c»ï¼ŒåŒ…括java.lang.Runnable接口或题目中指定的接口ã€?
• 知道命ä×o行参数是如何传递给¾cȝš„mainæ–ÒŽ³•çš„ã€?
• 知道哪些是JAVA的合法keyword。注意：考试中不会出现要你解释keyword和各¿Uå¸¸æ•°è¿™¿Uæ·±å¥¥çš„问题ã€?
• 明白如果没有昑ּåœ°èµ‹å€û|¼Œå„种变量或者数¾l„的默认值是什么ã€?
• 掌握所有原始数据类型的取å€ÆDŒƒå›ß_¼Œå¦‚何声明各种数据¾cÕdž‹ã€?

• 知道怎么样声明、创建和初始化各¿Uç±»åž‹çš„数组
• 知道怎么样声明类、内部类、方法、成员变量、静态变量和æ–ÒŽ³•å†…部变量åQŒåƈ会ä‹É用合法的修饰½W¦ï¼ˆå¦‚public,final,static,abstract,½{‰ç­‰åQ‰ã€‚了解这些修饰符单独使用或组合ä‹É用的含义åQŒåƈ且知道它们对于包作用域的影响ã€?
• 了解¾cȝš„构造器åQˆconstructoråQ?
• ¾l™å®šä¸€ä¸ªæ–¹æ³•ï¼Œèƒ½åˆ¤æ–­å®ƒçš„合法返回类åž?