1.
public class ReturnIt{
????? returnType methodA(byte x, double y){?? //line 2
??????????? return (short)x/y*2;
????? }
}
what is valid returnType for methodA in line 2?
答案:返回double類型,因為(short)x將byte類型強制轉(zhuǎn)換為short類型,與double類型運算,將會提升為double類型.
2.
1)? class Super{
2)????????? public float getNum(){return 3.0f;}
3)? }
4)
5)? public class Sub extends Super{
6)
7)? }
which method, placed at line 6, will cause a compiler error?
A. public float getNum(){return 4.0f;}
B. public void getNum(){}
C. public void getNum(double d){}
D. public double getNum(float d){return 4.0d;}
Answer:B
A屬于方法的重寫(重寫只存在于繼承關(guān)系中),因為修飾符和參數(shù)列表都一樣.B出現(xiàn)編譯錯誤,如下:
Sub.java:6: Sub 中的 getNum() 無法覆蓋 Super 中的 getNum()；正在嘗試使用不
兼容的返回類型
找到： void
需要： float
?? public void getNum(){}
?????????????? ^
1 錯誤
B既不是重寫也不是重載,重寫需要一樣的返回值類型和參數(shù)列表,訪問修飾符的限制一定要大于被重寫方法的訪問修飾符（public>protected>default>private）;
重載:必須具有不同的參數(shù)列表；
　　可以有不同的返回類型，只要參數(shù)列表不同就可以了；
　　可以有不同的訪問修飾符；
把其看做是重載,那么在java中是不能以返回值來區(qū)分重載方法的,所以b不對.
3.
public class IfTest{
??? public static void main(String args[]){
??????? int x=3;
??????? int y=1;
??????? if(x=y)
??????????? System.out.println("Not equal");
??????? else
??????????? System.out.println("Equal");
??? }
}
what is the result?
Answer:compile error 錯誤在與if(x=y) 中,應(yīng)該是x==y;? =是賦值符號,==是比較操作符
4. public class Foo{
? public static void main(String args[]){
? try{return;}
?? finally{ System.out.println("Finally");}
?? }
??? }
what is the result?
A. print out nothing
B. print out "Finally"
C. compile error
Answer:B?? java的finally塊會在return之前執(zhí)行,無論是否拋出異常且一定執(zhí)行.
5.public class Test{
?? public static String output="";
?? public static void foo(int i){
???? try {
?????? if(i==1){
???????? throw new Exception();
?????? }
?????? output +="1";
???? }
???? catch(Exception e){
?????? output+="2";
?????? return;
???? }
???? finally{
?????? output+="3";
???? }
???? output+="4";
?? }
?? public static void main(String args[]){
???? foo(0);
???? foo(1);
???? 24)??
?? }
}
what is the value of output at line 24? Answer:13423 如果你想出的答案是134234,那么說明對return的理解有了混淆,return是強制函數(shù)返回,本題就是針對foo(),那么當(dāng)執(zhí)行到return的話,output+="4"; 就不再執(zhí)行拉,這個函數(shù)就算結(jié)束拉.
6. public class IfElse{
??????? public static void main(String args[]){
??????????? if(odd(5))
??????????????? System.out.println("odd");
??????????? else
??????????????? System.out.println("even");
???????? }
???????? public static int odd(int x){return x%2;}??
???? }
???? what is output?
???? Answer:Compile Error
7. class ExceptionTest{
?????????? public static void main(String args[]){
???????????????? try{
?????????????????????? methodA();
???????????????? }
???????????????? catch(IOException e){
?????????????????????? System.out.println("caught IOException");
???????????????? }
???????????????? catch(Exception e){
??????????????????????? System.out.println("caught Exception");
???????????????? }
??????????? }
????? }
If methodA() throws a IOException, what is the result? (其實還應(yīng)該加上:import java.io.*;)
Answer:caught IOException 異常的匹配問題,如果2個catch語句換個位置,那就會報錯,catch只能是越來越大,意思就是說:catch的從上到下的順序應(yīng)該是:孫子異常->孩子異常->父親異常->老祖先異常.這么個順序.
8. int i=1,j=10;
??? do{
?????????? if(i++>--j) continue;
???? }while(i<5); (注意不要丟了這個分號呦)
After Execution, what are the value for i and j?
A. i=6 j=5
B. i=5 j=5
C. i=6 j=4
D. i=5 j=6
E. i=6 j=6
Answer:D
9. 1)public class X{
??? 2)?????? public Object m(){
??? 3)???????????? Object o=new Float(3.14F);
??? 4)???????????? Object[] oa=new Object[1];
??? 5)???????????? oa[0]=o;
??? 6)???????????? o=null;
??? 7)???????????? oa[0]=null;
??? ???????????? System.out.println(oa[0]);
??? 9)??????? }
? 10) }
which line is the earliest point the object a refered is definitely elibile
to be garbage collectioned?
A.After line 4?? B. After line 5? C.After line 6??
D.After line 7?? E.After line 9(that is,as the method returns)
Answer:D
如果 6) o=null 變成 o=9f? ,并且把7)去掉,那么8)將會輸出什么呢?
10.? 1)? interface Foo{
??????? 2)????? int k=0;
??????? 3)? }
??????? 4)? public class Test implements Foo{
??????? 5)?????? public static void main(String args[]){
??????? 6)???????????? int i;
??????? 7)???????????? Test test? = new Test();
??????? ???????????? i = test.k;
??????? 9)???????????? i = Test.k;
????? 10)???????????? i = Foo.k;
????? 11)???? }
????? 12) }
?? what is the result? Answer:compile successed and i=0 接口中的int k=0雖然沒有訪問修飾符,但在接口中默認(rèn)是static和final的
11. what is reserved words in java?
????? A. run
????? B. default
????? C. implement
????? D. import
????? Answer:B,D
12. public class Test{
?????????? public static void main(String[] args){
???????????????? String foo=args[1];
???????????????? Sring bar=args[2];
???????????????? String baz=args[3];
?????????? }
?????? }
java Test Red Green Blue
? what is the value of baz?
? A. baz has value of ""
? B. baz has value of null
? C. baz has value of Red
? D. baz has value of Blue
? E. baz has value of Green
? F. the code does not compile
? G. the program throw an exception
? Answer:G
分析:感覺原應(yīng)該多一些語句吧,至少應(yīng)該有紅綠藍(lán)的賦值語句之類的,才能叫java Test Red Green Blue 才能有后面的選項,所以現(xiàn)在感覺很奇怪,不過就這個樣子吧.這個問題在于:數(shù)組參數(shù)的理解,編譯程序沒有問題,但是運行這個程序就會出現(xiàn)問題,因為參數(shù)args沒有給他分配空間那么他的長度應(yīng)該是0,下面卻用拉args[1]........等等的語句,那么定會出現(xiàn)越界錯誤.
錯誤如下:Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
at Test.main(Test.java:4)

13. int index=1;
?????? int foo[]=new int[3];
?????? int bar=foo[index];
?????? int baz=bar+index;

? what is the result?
? A. baz has a value of 0
? B. baz has value of 1
? C. baz has value of 2
? D. an exception is thrown
? E. the code will not compile
? Answer:B?
分析:《thinking in java》中的原話：若類的某個成員是基本數(shù)據(jù)類型，即使沒有進(jìn)行初始化，java也會確保它獲得一個默認(rèn)值，如下表所示：
基本類型 默認(rèn)值
boolean false
char '\u0000'(null)
byte (byte)0
short (short)0
int 0
long 0L
float 0.0f
double 0.0d
千萬要小心：當(dāng)變量作為類的成員使用時，java才確保給定其默認(rèn)值，。。。。。（后面還有很多話，也很重要，大家一定要看完成，要不然還是不清楚）
14. which three are valid declaraction of a float?
?? A. float foo=-1;
?? B. float foo=1.0;
?? C. float foo=42e1;
?? D. float foo=2.02f;
?? E. float foo=3.03d;
?? F. float foo=0x0123;
Answer:A,D,F 分析：B錯誤，因為1.0在java中是double類型的，C，E錯誤同樣道理，都是double類型的
15. public class Foo{
???????????? public static void main(String args[]){
?????????????????????? String s;
?????????????????????? System.out.println("s="+s);
???????????? }
?????? }
what is the result?
Answer:compile error 分析：需要對s進(jìn)行初始化，和13題是不是矛盾呢：不矛盾，因為它不是基本類型，也不是類的成員，所以不能套用上述的確保初始化的方法。
16.?? 1) public class Test{
???????? 2)?????? public static void main(String args[]){
???????? 3)?????????? int i =0xFFFFFFF1;
???????? 4)?????????? int j=~i;
???????? 5)
???????? 6)?????? }
???????? 7) }
which is decimal value of j at line 5?
A. 0????? B.1??? C.14??? D.-15??? E. compile error at line 3? F. compile error at line 4
Answer:C? 分析：int是32位的（范圍應(yīng)該在-231~231-1），按位取反后，后4位是1110，前面的全部是0，所以肯定是14
17. float f=4.2F;
????? Float g=new Float(4.2F);
????? Double d=new Double(4.2);

Which are true?
A. f==g?? B. g==g?? C. d==f?? D. d.equals(f)? E d.equals(g)? F. g.equals(4.2);
Answer:B,E（網(wǎng)上的答案是B，E；我測試的結(jié)果是：true，true，false，false，fasle，fasle，所以答案是：A，B，還請各位大蝦明示）
分析：以下是我從網(wǎng)絡(luò)上找到的，但是感覺應(yīng)用到這個題目上反而不對拉，郁悶中，希望能給大家有所提示，要是你們明白拉，記得給我留言?。。簙
1.基本類型、對象引用都在棧中； 而對象本身在堆中；
2.“==“比的是兩個變量在棧內(nèi)存中的值，而即使變量引用的是兩個對象，“==”比的依舊是變量所擁有的“棧內(nèi)存地址值”；
3.equals()是每個對象與生俱來的方法，因為所有類的最終基類就是Object(除去Object本身)；而equals()是Object的方法之一，也就是說equals()方法來自O(shè)bject類。 觀察一下Object中equals()的source code：
public boolean equals(Object obj) { return (this == obj); }
注意：“return (this == obj)” this與obj都是對象引用，而不是對象本身。所以equals()的缺省實現(xiàn)就是比較“對象引用”是否一致，所以要比較兩個對象本身是否一致，須自己編寫代碼覆蓋Object類里的equals()的方法。來看一下String類的equals方法代碼：
public boolean equals(Object anObject){
if(this == anObject){
? return true;
}
if(anObject instanceof String){
? String anotherString = (String)anObject;
? int n = count;
? if(n == anotherString.count){
?? char v1[] = value;
?? char v2[] = anotherString.value;
?? int i = offset；
?? int j = anotherString.offset；
?? while(n-- != 0){
??? if(v1[i++] != v2[j++])
???? return false;
?? }
?? return true;
? }
}
return false;
}
18.? public class Equals{
??????????? public static void add3(Integer i){
??????????????? int val = i.intValue();
??????????????? val += 3;
??????????????? i = new Integer(val);
???????????? }
???????????? public static void main(String args[]){
???????????????? Integer i=new Integer(0);
???????????????? add3(i);
???????????????? System.out.println(i.intValue());
???????????? }
???????? }
what is the result?
A. compile fail?????? B.print out "0"????? C.print out "3"??
D.compile succeded but exception at line 3
Answer:B?? 分析:java只有一種參數(shù)傳遞方式,那就是值傳遞.(大家可以看我轉(zhuǎn)載的另一個同名文章,會讓大家豁然開朗)
19. public class Test{
　??????? public static void main(String[] args){
　　????????? System.out.println(6^3);
　　??? }
　?? }
　 what is output? Answer:5　分析: ^ is yi huo(計算機(jī)器上是Xor) ;異或的邏輯定義:真^真=假 真^假=真 假^真=真 假^假=假
20. public class Test{
　???????? public static void stringReplace(String text){
　　??????????? text=text.replace('j','l');
　???????? }
　???????? public static void bufferReplace(StringBuffer text){
　　??????????? text=text.append("c");
　　???? }
　???????? public static void main(String args[]){　
　　??????????? String textString=new String("java");
　　??????????? StringBuffer textBuffer=new StringBuffer("java");
　　??????????? stringReplace(textString);
　　??????????? bufferReplace(textBuffer);
　??????????????? System.out.println(textString+textBuffer);
　　?????? }
　　? }
what is the output?
Answer:javajavac
分析:根據(jù)我轉(zhuǎn)載的一篇文章<Java只有一種參數(shù)傳遞方式，那就是傳值>可以得出答案，不過還有幾個類似的題目，用該文章解釋不通，因為本人對java傳遞參數(shù)也一直沒有弄明白，所以，還請大蝦多多指教．
21. public class ConstOver{
　 　　　public ConstOver(int x, int y, int z){}
　? }
　 which two overload the ConstOver constructor?
　 A.ConstOver(){}
　 B.protected int ConstOver(){}　 //not overload ,but no a error
　 C.private ConstOver(int z, int y, byte x){}
　 D.public void ConstOver(byte x, byte y, byte z){}
　 E.public Object ConstOver(int x, int y, int z){}
Answer:A,C
分析：測試不通過的首先是B,E,因為要求有返回值,這2個選項沒有,要想通過編譯那么需要加上返回值,請注意如果加上返回值,單純看選項是沒有問題拉,可以針對題目來說,那就是錯之又錯拉,對于構(gòu)造器來說是一種特殊類型的方法,因為它沒有返回值.對于D選項在<java編程思想 第3版>91頁有詳細(xì)的介紹,空返回值,經(jīng)管方法本身不會自動返回什么,但可以選擇返回別的東西的,而構(gòu)造器是不會返回任何東西的,否則就不叫構(gòu)造器拉.
22. public class MethodOver{
　????????? public void setVar(int a, int b, float c){}
　? }
　 which overload the setVar?
　 A.private void setVar(int a, float c, int b){}
　 B.protected void setVar(int a, int b, float c){}
　 C.public int setVar(int a, float c, int b){return a;}
　 D.public int setVar(int a, float c){return a;}
Answer:A,C,D 分析:方法的重載,根據(jù)概念選擇,B是錯誤的,因為他們有相同的參數(shù)列表,所以不屬于重載范圍.
23. class EnclosingOne{
???????????? public class InsideOne{}
　?? }
?????? public class InnerTest{
　???????? public static void main(String args[]){
　???????? EnclosingOne eo=new EnclosingOne();
　???????? //insert code here
　???????? }
??????? }
??????? A.InsideOne ei=eo.new InsideOne();
??????? B.eo.InsideOne ei=eo.new InsideOne();
??????? C.InsideOne ei=EnclosingOne.new InsideOne();
??????? D.InsideOne ei=eo.new InsideOne();
??????? E.EnclosingOne.InsideOne ei=eo.new InsideOne();
Answer:E
24. What is "is a" relation?
? A.public interface Color{}
　? public class Shape{private Color color;}
? B.interface Component{}
　? class Container implements Component{ private Component[] children; }
? C.public class Species{}
　 public class Animal{private Species species;}　
? D.interface A{}
????? interface B{}
????? interface C implements A,B{}　 //syntex error
Answer:B 我沒有明白這個題目的意思,有人能告訴我嘛?
25. 1)package foo;
????? 2)
????? 3)public class Outer{
????? 4)??? public static class Inner{
????? 5)??? }
????? 6)}
? which is true to instantiated Inner class inside Outer?
? A. new Outer.Inner()
? B. new Inner()
Answer:B
if out of outerclass A is correct? 分析:在Outer內(nèi)部,B方式實例化內(nèi)部類的方法是正確的,如果在Outer外部進(jìn)行inner的實例化,那么A方法是正確的.
26. class BaseClass{
　??????? private float x=1.0f;
　??????? private float getVar(){return x;}
　?? }
????? class SubClass extends BaseClass{
　??????? private float x=2.0f;
　??????? //insert code
　 }
? what are true to override getVar()?
? A.float getVar(){
? B.public float getVar(){
? C.public double getVar(){
? D.protected float getVar(){
? E.public float getVar(float f){
Answer:A,B,D 分析:返回類型和參數(shù)列表必須完全一致,且訪問修飾符必須大于被重寫方法的訪問修飾符.
27. public class SychTest{
????????? private int x;
????????? private int y;
????????? public void setX(int i){ x=i;}
????????? public void setY(int i){y=i;}
????????? public Synchronized void setXY(int i){
?????????????? setX(i);
?????????????? setY(i);
????????? }
????????? public Synchronized boolean check(){
?????????????? return x!=y;??
????????? }
????? }
Under which conditions will? check() return true when called from a different class?
A.check() can never return true.
B.check() can return true when setXY is callled by multiple threads.
C.check() can return true when multiple threads call setX and setY separately.
D.check() can only return true if SychTest is changed allow x and y to be set separately.
Answer:C
分析:答案是C,但是我想不出來一個測試程序來驗證C答案.希望高手們給我一個測試的例子吧,萬分感謝..........
28. 1) public class X implements Runnable{
?????? 2)????????????? private int x;
?????? 3)????????????? private int y;
?????? 4)????????????? public static void main(String[] args){
?????? 5)?????????????????????????????? X that =new X();
?????? 6)????????????????????????????? (new Thread(that)).start();
?????? 7)????????????????????????????? (new Thread(that)).start();
???????????????????????? }
?????? 9)????????????? public synchronized void run(){
???? 10)????????????????????????????? for(;;){
???? 11)????????????????????????????????????????? x++;
???? 12)????????????????????????????????????????? y++;
???? 13)????????????????????????????????????????? System.out.println("x="+x+",y="+y);
???? 14)?????????????????????????????? }
???? 15)???????????????? }
???? 16) }??
????? what is the result?
????? A.compile error at line 6
????? B.the program prints pairs of values for x and y that are always the same on the same time
????? Answer:B 分析：我感覺會出現(xiàn)不相等的情況，但是我說不出為什么會相等。線程方面，還有好多路要走啊，咳
29. class A implements Runnable{
????????????? int i;
????????????? public void run(){
????????????????? try{
??????????????????????? Thread.sleep(5000);
???????????????????????? i=10;
????????????????? }catch(InterruptedException e){}
????????????? }
????????????? public static void main(String[] args){
????????????????? try{
?????????????????????? A a=new A();
????????????????????? Thread t=new Thread(a);
?????????????????????? t.start();
?????????????????????? 17)
??????????????????????? int j=a.i;
??????????????????????? 19)
????????????? }catch(Exception e){}
??????? }
??? }
what be added at line line 17, ensure j=10 at line 19?
A. a.wait();?? B.? t.wait();?? C. t.join();?? D.t.yield();??? E.t.notify();??? F. a.notify();???? G.t.interrupt();
Answer:C
30. Given an ActionEvent, how to indentify the affected component?
??? A.getTarget();
??? B.getClass();
??? C.getSource();?? //public object
??? D.getActionCommand();
Answer:C
31. import java.awt.*;
public class X extends Frame{
??? public static void main(String[] args){
????? X x=new X();
????? x.pack();
????? x.setVisible(true);
??? }
??? public X(){
????? setLayout(new GridLayout(2,2));
?????
????? Panel p1=new Panel();
????? add(p1);
????? Button b1=new Button("One");
????? p1.add(b1);
?????
????? Panel p2=new Panel();
????? add(p2);
????? Button b2=new Button("Two");
????? p2.add(b2);
??????
????? Button b3=new Button("Three");
????? p2.add(b3);
?????
????? Button b4=new Button("Four");
????? add(b4);
?? }
}
when the frame is resized,
A.all change height??? B.all change width?? C.Button "One" change height
D.Button "Two" change height? E.Button "Three" change width
F.Button "Four" change height and width
Answer:F
32. 1)public class X{
? 2)??? public static void main(String[] args){
? 3)???? String foo="ABCDE";
? 4)???? foo.substring(3);
? 5)???? foo.concat("XYZ");
? 6)??? }
? 7)?? }
? what is the value of foo at line 6?
Answer:ABCDE
33. How to calculate cosine 42 degree?
? A.double d=Math.cos(42);
? B.double d=Math.cosine(42);
? C.double d=Math.cos(Math.toRadians(42));
? D.double d=Math.cos(Math.toDegrees(42));
? E.double d=Math.toRadious(42);
Answer:C
34. public class Test{
?? public static void main(String[] args){
?? StringBuffer a=new StringBuffer("A");
?? StringBuffer b=new StringBuffer("B");
?? operate(a,b);
?? System.out.pintln(a+","+b);
??? }
?? public static void operate(StringBuffer x, StringBuffer y){
??? x.append(y);
??? y=x;
?? }
?? }
?? what is the output?
Answer:AB,B 分析：這道題的答案是AB,B,網(wǎng)上有很多答案給錯啦，大家注意啊。
35.? 1) public class Test{
?????? 2)???? public static void main(String[] args){
?????? 3)?????? class Foo{
?????? 4)??????????? public int i=3;
?????? 5)??????? }
?????? 6)??????? Object o=(Object)new Foo();
?????? 7)??????? Foo foo=(Foo)o;
?????????????????? System.out.println(foo.i);
?????? 9)???? }
???? 10) }
? what is result?
? A.compile error at line 6
? B.compile error at line 7
? C.print out 3
Answer:C

36. public class FooBar{
?? public static void main(String[] args){
??? int i=0,j=5;
? 4) tp:? for(;;i++){
???????? for(;;--j)
??????? if(i>j)break tp;
?????? }
?? System.out.println("i="+i+",j="+j);
?? }
?? }
? what is the result?
? A.i=1,j=-1??? B. i=0,j=-1? C.i=1,j=4??? D.i=0,j=4??
? E.compile error at line 4
Answer:B
37. public class Foo{
???????????? public static void main(String[] args){
???????????????????????? try{System.exit(0);}
???????????????????????? finally{System.out.println("Finally");}
???????????? }
?????? }
?? what is the result?
?? A.print out nothing
?? B.print out "Finally"
Answer:A
system.exit(0) has exit
38. which four types of objects can be thrown use "throws"?
? A.Error
? B.Event
? C.Object
? D.Excption
? E.Throwable
? F.RuntimeException
Answer:A,D,E,F
分析:throw，例如：throw new IllegalAccessException("demo");是一個動作。
而throws則是異常塊兒的聲明。所以感覺題目應(yīng)該是“throw”
39. 1)public class Test{
?????? 2)???? public static void main(String[] args){
?????? 3)???????? unsigned byte b=0;
?????? 4)???????? b--;
?????? 5)
?????? 6)???? }
?????? 7) }
what is the value of b at line 5?
A.-1?? B.255? C.127? D.compile fail? E.compile succeeded but run error
Answer:D
40. public class ExceptionTest{
??????????? class TestException extends Exception{}
??????????? public void runTest() throws TestException{}
??????????? public void test() /* point x */ {
??????????????????? runTest();
??????????? }
?????? }
At point x, which code can be add on to make the code compile?
A.throws Exception?? B.catch (Exception e)
Answer:A
41. String foo="blue";
?????? boolean[] bar=new boolean[1];
?????? if(bar[0]){
????????? foo="green";
?????? }
what is the value of foo?
A.""? B.null? C.blue?? D.green
Answer:C
42. public class X{
?????????? public static void main(String args[]){
???????????????? Object o1=new Object();
???????????????? Object o2=o1;
???????????????? if(o1.equals(o2)){
????????????????????? System.out.prinln("Equal");
????????????????? }
??????????? }
?????? }
what is result?
Answer:Equal

java試題解析