判断题
1-1 JLable can contain other components.
false
1-2 A local class or anonymous class cannot access all local variables from the enclosing method.
true
1-3 Using JPanel p = new JPanel(); BoxLayout b1 = new BoxLayout(p, BoxLayout.X_AXIS); can set the BoxLayout for Panel p.
false
单选题
2-1 Which one below is the correct signature of InputStream.read() ?
byte read()
char read()
int read()
long read()
C
2-2 Which of these methods will make a thread leave the running state, and the method is not static?
notify()
Thread.KillThread()
yield()
wait()
D
2-3 Which one below is NOT a valid Java identifier?
2-4 Choose the best fill in the blanks.
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| class Hello2017
{ public static void main(String[] args)
{
(__
}
}
class Century extends Thread
{ String m=”Hello”;
Century(String m){
this.m=m;
}
public void run() {
System.out.println(m);
}
}
|
new Century(“Hello”).start();
new Thread(“Hello”).start();
new Century(new Thread()).start();
new Thread(new Century()).start();
A
2-5 For object o and class C , which expression below is the right way to test if o is an object of C?
C.isInstance(o)
o.class == C
o instanceof C
o.getClass() == C
not D
2-6
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| int x=0x80000000;
if (x==-x)
System.out.println("OK");
else
System.out.println("NOT");
|
output:
2-7 Which of the following is NOT correct?
A Generic Type Parameter of a Class Is Not Allowed in a Static Context
Cannot Create an Instance of a Generic Type. (i.e., new E()).
Generic Array Creation is Not Allowed. (i.e., new E[100]).
Exception Classes Can be Generic.
not C
2-8
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2
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4
| List<Double> ls = new ArrayList<Double>();
List<?> lo = ls;
lo.add(new Object());
String s = ls.get(0);
|
It compiles but exception raises at line 3
It does not compile
It compiles but exception raises at line 2
It compiles but exception raises at line 4
B
填空题
3-1
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| public class Test {
public static void main(String[] args) {
CloneT c = new CloneT();
CloneT t = (CloneT)c.clone();
t.str = "t";
t.b.setA(3);
System.out.println(t==c);
System.out.println(t.b==c.b);
System.out.println(c.toString()+t.toString());
}
}
class Base implements Cloneable{
int a = 1;
public String toString(){
return String.valueOf(a);
}
public void setA(int a){
this.a = a;
}
}
class CloneT implements Cloneable{
transient int i = 1;
private int pi = 1;
static int num = 0;
String str = "c";
Base b = new Base();
public CloneT(){
num++;
}
public Object clone(){
try{
return super.clone();
}catch(CloneNotSupportedException e){
System.out.println("clone not supported!");
return null;
}
}
public String toString(){
return String.valueOf(i) + String.valueOf(pi) + String.valueOf(num) + str + String.valueOf(b);
}
}
|
false
true
111c3111t3
3-2
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3
| IntStream.range(2, 10).
filter(x->IntStream.range(2, x).filter(k->x%k==0).sum()>0).
sum()
|
27
3-3
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| class A {
public int data=1;
private int pd = 2;
public void print() {
System.out.println(data+pd);
f();
}
protected void f() {
System.out.println(1);
}
}
class B extends A {
public int data=3;
private int pd = 4;
public void print() {
super.print();
System.out.println(data+pd);
}
protected void f() {
System.out.println(2);
}
}
public class TestAB {
public static void main(String[] args) {
A a = new B();
a.print();
}
}
|
3
2
7
3-4
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| public class Test {
public static void main(String[] args) {
Integer a = new Integer(127);
Integer b = 127;
Integer c = Integer.valueOf("127");
System.out.println(a==b);
System.out.println(a==c);
System.out.println(b==c);
}
}
|
false
false
true
to be done:
解释