⑴ （java类和对象练习）.
importjava.util.Arrays;
importjava.util.Comparator;
classStudent
{
publicStringstuNo;
publicStringstuName;
publicintstuAge;
publicStudent(StringstuNo,StringstuName,intstuAge)
{
this.stuNo=stuNo;
this.stuName=stuName;
this.stuAge=stuAge;
}
publicvoidaddAge()
{
stuAge++;
}
publicStringtoString()
{
return"No:"+让咐stuNo+"Name:"+stuName+"Age:"+stuAge;
}
}
<稿衫Student>
{
@Override
publicintcompare(Studento1,Studento2)
{
//TODOAuto-generatedmethodstub
returno1.stuNo.compareTo(o2.stuNo);
}
}
publicclassTest3
{
publicstaticvoidmain(String[]args)
{
Student[]students=newStudent[5];
students[0]=newStudent("1003","a",12);
students[1]=newStudent("1002","b",13);
students[2]=newStudent("1004","c",14);
students[3]=newStudent("1001","d",15);
students[4]键滑腔=newStudent("1005","e",16);
Arrays.sort(students,newStudentOrder());
intcount=0;
for(inti=0;i<5;i++)
{
System.out.println(students[i]);
students[i].addAge();
if(students[i].stuAge>20)
count++;
}
System.out.println("大于20岁的人数:"+count);
}
}
⑵ JAVA程序题~关于类和对象
所谓对象就是真实世界中的实体唯辩闹，对象与实体是一一对应的，也就是说现实灶颂世界中每一个实体都是一个对象，它是一种具体的概念。类是具备某些共同特征指罩的实体的集合，它是一种抽象的概念，用程序设计的语言来说，类是一种抽象的数据类型，它是对所具有相同特征实体的抽象。
⑶ 用JAVA编程 类与对象的基础题
class Phone{
private String phonenumber;
public void setPhonenumber(String phonenumber){
this.phonenumber=phonenumber;
}
public String getPhonenumber(){
return phonenumber;
}
public void recCall(){
System.out.println("接到一个电话");
}
public void telCall(){
System.out.println("拨出一个电话");
}
}class Fixedphone extends Phone{
private String phonenumber;//号码是私有，设置为private，不可继承
public void recCall(){
System.out.println("以"+this.phonenumber+"呼出了一个电话"); //重载了父类的recCall
}
}class Cordlessphone extends Fixedphone{
private String phonenumber;
public void info(){
System.out.println("这是无绳电话的信息");
}
}interface Moveable{
public void moveinfo();
}class Mobilephone extends Phone implements Moveable{
private String phonenumber;
public void moveinfo(){
System.out.println("我实现了可移动性");
}
}public class PhoneTest{
public static void main(String a[]){
Phone[] p=new Phone[5];
Phone p1=new Phone();
p1.setPhonenumber("123456789");
p[0]=p1;
Phone p2=new Phone();
p2.setPhonenumber("987654321");
p[1]=p2;
Mobilephone mp=new Mobilephone();
mp.setPhonenumber("11111");
p[2]=mp;
Fixedphone fp=new Fixedphone();
fp.setPhonenumber("22222");
p[3]=fp;
Cordlessphone cp=new Cordlessphone();
cp.setPhonenumber("33333");
p[4]=cp;
for(int i=0;i<p.length;i++){
System.out.println(p[i].getPhonenumber());
} p[4]=p[1];
System.out.println(p[4].getPhonenumber());
}} 写的不是很好，希望对你有帮助噶
⑷ 关于java的问题:类与对象
类是一组数据和函数的集合，只是抽象的概念，它的作用就是生成对象，它生成对象后，就为模答橡这个对象分了一块存储区，类可以生成无限多个对象，每个对象都有自己的存储区，在类里定义的数据和函数在这个对象里都有了
类生成的不同对象都有自己不同的存储区，所以每个对象的数据和函数都存在不同的地方，改变了这个对象的数据不会印象另一个对象的数据，但是加了static后，举猛数旦旁据和函数就是静态的了，静态的数据或函数存在一个存储区，因为是存在一个地方，所以所有对象对这个数据是共有的，只要它一改变，所有对象的这个数据都会改变
⑸ 谁能提供JAVA 类和对象的练习题!!
Question No: 1
public class test (
2. public static void main (String args[]) {
3. int i = 0xFFFFFFF1;
4. int j = ~i;
5.
6. }
7. )
What is the decimal value of j at line 5?
A. 0
B. 1
C. 14
D. –15
E. An error at line 3 causes compilation to fail.
F. An error at line 4 causes compilation to fail.
答案: C
Question No: 2
Given:
Integer i = new Integer (42);
Long 1 = new Long (42);
Double d = new Double (42.0);
Which two expressions evaluate to True? (Choose Two)
A. (i ==1)
B. (i == d)
C. (d == 1)
D. (i.equals (d))
E. (d.equals (i))
F. (i.equals (42))
答案: D, E
Question No: 3
Exhibit :
1. public class test (
2. private static int j = 0;
3.
4. private static boolean methodB(int k) (
5. j += k;
6. return true;
6. )
7.
8. public static void methodA(int i) {
9. boolean b:
10. b = i < 10 | methodB (4);
11. b = i < 10 || methodB (8);
12. }
13.
14. public static void main (String args[] ) (
15. methodA (0);
16. system.out.printIn(j);
17. )
18. )
What is the result?
A. The program prints “0”
B. The program prints “4”
C. The program prints “8”
D. The program prints “12”
E. The code does not complete.
答案: B
Question No: 4
Given
1. Public class test (
2. Public static void main (String args[]) (
3. System.out.printIn (6 ^ 3);
4. )
5. )
What is the output?
答案: 5
Question No: 5
Given:
1. public class Foo {
2. public static void main (String [] args) {
3. StringBuffer a = new StringBuffer (“A”);
4. StringBuffer b = new StringBuffer (“B”);
5. operate (a,b);
6. system.out.printIn{a + “,” +b};
7. }
8. static void operate (StringBuffer x, StringBuffer y) {
9. x.append {y};
10. y = x;
11. }
12. }
What is the result?
A. The code compiles and prints “A,B”.
B. The code compiles and prints “A,A”.
C. The code compiles and prints “B,B”.
D. The code compiles and prints “AB,B”.
E. The code compiles and prints “AB,AB”.
F. The code does not compile because “+” cannot be overloaded for StringBuffer.
答案: D
Question No: 6
Exhibit:
1. Public class test (
2. Public static void stringReplace (String text) (
3. Text = text.replace (‘j’ , ‘i’);
4. )
5.
6. public static void bufferReplace (StringBuffer text) (
7. text = text.append (“C”)
8. )
9.
10. public static void main (String args[]) (
11. String textString = new String (“java”);
12. StringBuffer text BufferString = new StringBuffer (“java”);
13.
14. stringReplace (textString);
15. BufferReplace (textBuffer);
16.
17. System.out.printIn (textString + textBuffer);
18. )
19. )
What is the output?
答案: JAVAJAVA
Question No: 7
Exhibit:
1. public class test {
2. public static void add3 (Integer i) }
3. int val = i.intValue ( );
4. val += 3;
5. i = new Integer (val);
6. )
7.
8. public static void main (String args [ ] ) {
9. Integer i = new Integer (0);
10. add3 (i);
11. system.out.printIn (i.intValue ( ) );
12. }
13. )
What is the result?
A. Compilation will fail.
B. The program prints “0”.
C. The program prints “3”.
D. Compilation will succeed but an exception will be thrown at line 3.
答案: B
Question No: 8
Given:
1. public class ConstOver {
2. public ConstOver (int x, int y, int z) {
3. }
4. }
Which two overload the ConstOver constructor? (Choose Two)
A. ConstOver ( ) { }
B. Protected int ConstOver ( ) { }
C. Private ConstOver (int z, int y, byte x) { }
D. Public Object ConstOver (int x, int y, int z) { }
E. Public void ConstOver (byte x, byte y, byte z) { }
答案: A, C
Question No: 9
Given:
1. public class MethodOver {
2. public void setVar (int a, int b, float c) {
3. }
4. }
Which two overload the setVar method? (Choose Two)
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, int b, float c) (return a;)
E. Protected float setVar (int a, int b, float c) (return c;)
答案: A, C
Question No: 10
Given:
1. class BaseClass {
2. Private float x = 1.0f ;
3. protected float getVar ( ) ( return x;)
4. }
5. class Subclass extends BaseClass (
6. private float x = 2.0f;
7. //insert code here
8. )
Which two are valid examples of method overriding? (Choose Two)
A. Float getVar ( ) { return x;}
B. Public float getVar ( ) { return x;}
C. Float double getVar ( ) { return x;}
D. Public float getVar ( ) { return x;}
E. Public float getVar (float f ) { return f;}
答案: B, D
Question No: 11
Which two demonstrate an “is a” relationship? (Choose Two)
A. public interface Person { }
public class Employee extends Person { }
B. public interface Shape { }
public class Employee extends Shape { }
C. public interface Color { }
public class Employee extends Color { }
D. public class Species { }
public class Animal (private Species species;)
E. interface Component { }
Class Container implements Component (
Private Component[ ] children;
)
答案: D, E
Question No: 12
Which statement is true?
A. An anonymous inner class may be declared as final.
B. An anonymous inner class can be declared as private.
C. An anonymous inner class can implement multiple interfaces.
D. An anonymous inner class can access final variables in any enclosing scope.
E. Construction of an instance of a static inner class requires an instance of the enclosing outer class.
答案: D
Question No 13
Given:
1. package foo;
2.
3. public class Outer (
4. public static class Inner (
5. )
6. )
Which statement is true?
A. An instance of the Inner class can be constructed with “new Outer.Inner ()”
B. An instance of the inner class cannot be constructed outside of package foo.
C. An instance of the inner class can only be constructed from within the outer class.
D. From within the package bar, an instance of the inner class can be constructed with “new inner()”
答案: A
Question No 14
Exhibit:
1. public class enclosingone (
2. public class insideone{}
3. )
4. public class inertest(
5. public static void main (string[]args)(
6. enclosingone eo= new enclosingone ();
7. //insert code here
8. )
9. )
Which statement at line 7 constructs an instance of the inner class?
A. InsideOnew ei= eo.new InsideOn();
B. Eo.InsideOne ei = eo.new InsideOne();
C. InsideOne ei = EnclosingOne.new InsideOne();
D. EnclosingOne.InsideOne ei = eo.new InsideOne();
答案: D
Question No 15
Exhibit:
1. interface foo {
2. int k = 0;
3. }
4.
5. public class test implements Foo (
6. public static void main(String args[]) (
7. int i;
8. Test test = new test ();
9. i= test.k;
10.i= Test.k;
11.i= Foo.k;
12.)
13.)
14.
What is the result?
A. Compilation succeeds.
B. An error at line 2 causes compilation to fail.
C. An error at line 9 causes compilation to fail.
D. An error at line 10 causes compilation to fail.
E. An error at line 11 causes compilation to fail.
答案: A
Question No 16
Given:
1. //point X
2. public class foo (
3. public static void main (String[]args) throws Exception {
4. printWriter out = new PrintWriter (new
5. java.io.outputStreamWriter (System.out), true;
6. out.printIn(“Hello”);
7. )
8. }
Which statement at PointX on line 1 allows this code to compile and run?
A. Import java.io.PrintWriter;
B. Include java.io.PrintWriter;
C. Import java.io.OutputStreamWriter;
D. Include java.io.OutputStreamWriter;
E. No statement is needed.
答案: A
Question No 17
Which two statements are reserved words in Java? (Choose Two)
A. Run
B. Import
C. Default
D. Implement
答案: B, C
Question No 18
Which three are valid declarations of a float? (Choose Three)
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;
答案: A, D, F
Question No 19
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Question No 19
Given:
8. int index = 1;
9. boolean[] test = new Boolean[3];
10. boolean foo= test [index];
What is the result?
A. Foo has the value of 0.
B. Foo has the value of null.
C. Foo has the value of true.
D. Foo has the value of false.
E. An exception is thrown.
F. The code will not compile.
答案: D
Question No 20
Given:
1. public class test(
2. public static void main(string[]args){
3. string foo = args [1];
4. string foo = args [2];
5. string foo = args [3];
6. }
7. )
And command line invocation:
Java Test red green blue
What is the result?
A. Baz has the value of “”
B. Baz has the value of null
C. Baz has the value of “red”
D. Baz has the value of “blue”
E. Bax has the value of “green”
F. The code does not compile.
G. The program throws an exception.
答案: G
Question No 21
Given:
8. int index = 1;
9. int [] foo = new int [3];
10.int bar = foo [index];
11.int baz = bar + index;
What is the result?
A. Baz has the value of 0
B. Baz has the value of 1
C. Baz has the value of 2
D. An exception is thrown.
E. The code will not compile.
答案: B
Question No 22
Given:
1. public class foo {
2. public static void main (String[]args) {
3. String s;
4. system.out.printIn (“s=” + s);
5. }
6. }
What is the result?
A. The code compiles and “s=” is printed.
B. The code compiles and “s=null” is printed.
C. The code does not compile because string s is not initialized.
D. The code does not compile because string s cannot be referenced.
E. The code compiles, but a NullPointerException is thrown when toString is called.
答案: C
Question No 23
Which will declare a method that forces a subclass to implement it?
A. Public double methoda();
B. Static void methoda (double d1) {}
C. Public native double methoda();
D. Abstract public void methoda();
E. Protected void methoda (double d1){}
答案: D
Question No 24
You want subclasses in any package to have access to members of a superclass. Which is the most
restrictive access modifier that will accomplish this objective?
A. Public
B. Private
C. Protected
D. Transient
E. No access modifier is qualified
答案: C
Question No 25
Given:
1. abstract class abstrctIt {
2. abstract float getFloat ();
3. }
4. public class AbstractTest extends AbstractIt {
5. private float f1= 1.0f;
6. private float getFloat () {return f1;}
7. }
What is the result?
A. Compilation is successful.
B. An error on line 6 causes a runtime failure.
C. An error at line 6 causes compilation to fail.
D. An error at line 2 causes compilation to fail.
答案: C
Question No 26
Exhibit:
1. public class test(
2. public int aMethod()[
3. static int i=0;
4. i++;
5. return I;
6. ]
7. public static void main (String args[]){
8. test test = new test();
9. test.aMethod();
10.int j = test.aMethod();
11.System.out.printIn(j);
12.}
13.)
What is the result?
A. Compilation will fail.
B. Compilation will succeed and the program will print “0”
C. Compilation will succeed and the program will print “1”
D. Compilation will succeed and the program will print “2”
答案: D
Question No 27
Given:
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) {retrun 4.0f; }
答案: B
Question No 28
Which declaration prevents creating a subclass of an outer class?
A. Static class FooBar{}
B. Private class FooBar{}
C. Abstract public class FooBar{}
D. Final public class FooBar{}
E. Final abstract class FooBar{}
答案: D
Question No 29
Given:
1. byte [] arry1, array2[];
2. byte array3 [][];
3. byte[][] array4;
If each array has been initialized, which statement will cause a compiler error?
A. Array2 = array1;
B. Array2 = array3;
C. Array2 = array4;
D. Both A and B
E. Both A and C
F. Both B and C
答案: F
Question No 30
Exhibit:
1. class super (
2. public int I = 0;
3.
4. public super (string text) (
5. I = 1
6. )
7. )
8.
9. public class sub extends super (
10. public sub (string text) (
11. i= 2
12. )
13.
14. public static void main (straing args[]) (
15. sub sub = new sub (“Hello”);
16. system.out. PrintIn(sub.i);
17. )
18. )
What is the result?
A. Compilation will fail.
B. Compilation will succeed and the program will print “0”
C. Compilation will succeed and the program will print “1”
D. Compilation will succeed and the program will print “2”
答案: A
Question No 31
Given:
1. public class returnIt (
2. returnType methodA(byte x, double y) (
3. return (short) x/y * 2;
4. )
5. )
What is the valid returnType for methodA in line 2?
A. Int
B. Byte
C. Long
D. Short
E. Float
F. Double
答案: F
Question No 32
Given the ActionEvent, which method allows you to identify the affected component?
A. GetClass.
B. GetTarget.
C. GetSource.
D. GetComponent.
E. GetTargetComponent.
答案: C
Question No 33
Which is a method of the MouseMotionListener interface?
A. Public void mouseMoved(MouseEvent)
B. Public boolean mouseMoved(MouseEvent)
C. Public void mouseMoved(MouseMotionEvent)
D. Public boolean MouseMoved(MouseMotionEvent)
E. Public boolean mouseMoved(MouseMotionEvent)
答案: A
⑹ 在Java中,以下关于类与对象描述错误的是().（选择二项）
b和c错误，选bc，b和c反了，应该是类是对象的一种抽象，对象是类的一个实例