How do objects pass&...

单项选择题How do objects pass messages in Java？（）

A.They pass messages by modifying each other’s member variables
B.They pass messages by modifying the static member variables of each other’s classes
C.They pass messages by calling each other’s instance member methods
D.They pass messages by calling static member methods of each other’s classes.

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1.多项选择题 Given that Thing is a class， how many objects and reference variables are created by the following code？（）
Thing item， stuff；
item = new Thing（）；
Thing entity = new Thing（）；

A.One object is created
B.Two objects are created
C.Three objects are created
D.One reference variable is created
E.Two reference variables are created
F.Three reference variables are created.

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2.单项选择题 Which line contains a constructor in this class definition？（）
public class Counter { // （1）
int current， step；
public Counter（int startValue， int stepValue） { // （2）
set（startValue）；
setStepValue（stepValue）； }
public int get（） { return current； } // （3）
public void set（int value） { current = value； } // （4）
public void setStepValue（int stepValue） { step = stepValue； } // （5） }

A.Code marked with （1） is a constructor
B.Code marked with （2） is a constructor
C.Code marked with （3） is a constructor
D.Code marked with （4） is a constructor
E.Code marked with （5） is a Constructor

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3.单项选择题An instance member（）

A.is also called a static member
B.is always a variable
C.is never a method
D.belongs to a single instance， not to the class as a whole
E.always represents an operation

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4.单项选择题An object is（）

A.what classes are instantiated from.
B.an instance of a class.
C.a blueprint for creating concrete realization of abstractions.
D.a reference to an attribute.
E.a variable.

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5.单项选择题A method is（）

A.an implementation of an abstraction.
B.an attribute defining the property of a particular abstraction.
C.a category of objects.
D.an operation defining the behavior for a particular abstraction.
E.a blueprint for making operations.

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6.单项选择题 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；
10. return o；
9. }
10. }
When is the float object created in line 3， eligible for garbage collection？（）

A. Just after line 5.
B. Just after line 6.
C. Just after line 7.
D. Just after line 8（that is， as the method returns）.

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7.多项选择题 public class MethodOver {
private int x， y；
private float z；
public void setVar（int a， int b， float c）{
x = a；
y = b；
z = c；
}
}
Which two overload the setVar method？（）

A. void setVar （int a， int b， float c）{ x = a； y = b； z = c； }
B. public void setVar（int a， float c， int b） { setVar（a， b， c）； }
C. public void setVar（int a， float c， int b） { this（a， b， c）； }
D. public void setVar（int a， float b）{ x = a； z = b； }
E. public void setVar（int ax， int by， float cz） { x = ax； y = by； z = cz； }

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8.单项选择题 1. class A {
2. public String toString （） {
3. return “4”；
4. }
5. }
6. class B extends A {
7. public String toString （） {
8. return super.toString（） + “3”；
9. }
10. }
11. public class Test {
12. public static void main（String[]args） {
13. System.out.printIn（new B（））；
14. }
15. }
What is the result？（）

A. Compilation succeeds and 4 is printed.
B. Compilation succeeds and 43 is printed.
C. An error on line 9 causes compilation to fail.
D. An error on line 14 causes compilation to fail.
E. Compilation succeeds but an exception is thrown at line 9.

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9.多项选择题Which two demonstrate encapsulation of data？（）

A. Member data have no access modifiers.
B. Member data can be modified directly.
C. The access modifier for methods is protected.
D. The access modifier to member data is private.
E. Methods provide for access and modification of data.

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10.单项选择题 public class Test {
public static void main （String [] args） {
string foo = “blue”；
string bar = foo；
foo = “green”；
System.out.printIn（bar）；
}
}
What is the result？（）

A. An exception is thrown.
B. The code will not compile.
C. The program prints “null”
D. The program prints “blue”
E. The program prints “green”

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