关于SCJP1.4考试的一些需要注意的地方(二)

王朝java/jsp·作者佚名  2006-01-09
窄屏简体版  字體: |||超大  

接上文:

21.An instance sl of a class S that extends a class B,where B declares the protected member and where sl is referring to one of the following:

1.its own copy of the proteched member inherited from B

2.a copy of the protected member owned by another instance S2 fo S (and therefore inherited from B)

3.a copy of the protected member owned by an instance of a subclass of S

22. null false true 不是保留字

23.Float f1=0.0f;

Float f2=-0.0f

Double d1=0.0

Double d2=-0.0

Int i=0

F1=f2=d1=d2=i

24. char a=’\u0061’;

Char \u0061=’a’;

Ch\u0061r \u0061=’\u0061’

25. methodA(){

int I,j;

if(true){i=1;}

if(i==1){j=2;}

System.out.println(i); (right)

System.out.println(j); (wrong)

}

Reason :

If the java compiler can immediately determine the value of Boolean expression within an if() statement,it will not generate code to evaluate the expression at runtime,if the compiler can determine that the Boolean expression is always false,it will not generate code for the corresponding compound statement.

26. constructor and abstract method can not be declared static final sychnorized native or strictfp

27. final 变量必须赋值,否则编译无法通过

28. int i=j; int j=1 (wrong)

int i=j; static int j=1; (right) 因为static初始化早

29. int []a={1,2}

int []b=(int[])a.clone(); 此时: a<>b

30. stclass s=new stclass();

s=null;

s.amethod(); //valid only if the amethod() is static one

31. String x=new String();

String y=new String(“”);

Both x and y creat an empty string

32 min(-0.0,0.0)=-0.0

33 class A{}

class B extends A{}

class C extends A{}

A a=new A();

B b=new B();

C c=new C();

Compiler runtime

a=b right right

b=c; wrong wrong

b=(b)c wrong wrong

b=(b)a; right may be wrong

b=a; wrong wrong

a=(a)b; right right

34. int x=6; double y=9.7;

System.our.println((x<y)?9:8.6); 输出9.0

System.our.println((6<9.7)?9:8.6); 输出9

35.boolean b=new boolean(“true”);

boolean b2=new boolean(“asdfad”);

则 b=true b2=false

36.Synchnorized ―――

class method。instance method。a part in method

37.switch(k) k―――byte char int

38.wait must be called inside sychronized code

39. class A{

static{

System.out.println(“sdfasd”);

}

}

此部分并不是实例化一次就执行一次,而是load到jvm时执行一次,即 java A时执行一次

40 int a=(octal)5; octal不是合法字符

 
 
 
免责声明:本文为网络用户发布,其观点仅代表作者个人观点,与本站无关,本站仅提供信息存储服务。文中陈述内容未经本站证实,其真实性、完整性、及时性本站不作任何保证或承诺,请读者仅作参考,并请自行核实相关内容。
 
 
© 2005- 王朝網路 版權所有 導航