SCJP认证试题(十三)

1public class A{
2	private int counter = 0;
3	
4	public static int getInstanceCount(){
5		return counter;
6	}
7	
8	public A(){
9		counter++;
10	}
11}


Given this code from class B:

25	A a1 = new A();
26	A a2 = new A();
27	A a3 = new A();
28	System.out.println(A.getInstanceCount());

What is the result?


A Compilation of class A fails
B Line 28 prints the value 3 to System.out
C Line 28 prints the value 1 to System.out
D A runtime error occurs when line 25 executes
E Compilation fails because of an error in line 28


Answer: A

10	class One{
11		void foo(){}
12	}
13	class Two extends One{
14		//insert method here
15	}

Which three methods,inserted individually at line 14, will correctly complete class Two?(Choose three)



A int foo(){/*mode code here*/}
B void foo(){/*more code here*/}
C public void foo(){/*more code here*/}
D private void foo(){/*more code here*/}
E protected void foo(){/*more code here*/}


Answer: B C E

1	public interface A{
2		String DEFAULT_GREETING = "Hello World";
3		public void method1();
4	}

A programmer wants to create an interface called B that has A as its parent.
Which interface declaration is correct?


A public interface B extends A{}
B public interface B implements A{}
C public interface B instanceOf A{}
D public interface B inheritsFrom A{}


Answer : A

11	public abstract class Shape{
12		int x;
13		int y;
14		public abstract void draw();
15		public void setAnchor(int x, int y){
16			this.x = x;
17			this.y = y;
18		}
19	}

And a class Circle that extends and fully implements the Shape class.
Which is correct?


A Shape s = new Shape();
s.setAnchor(10,10);
s.draw();
B Circle c = new Shape();
c.setAnchor(10,10);
c.draw();
C Shape s = new Circle();
s.setAnchor(10,10);
s.draw();
D Shape s = new Circle();
s->setAnchor(10,10);
s->draw();
E Circle c = new Circle();
c.Shape.setAnchor(10,10);
c.shape.draw();


Answer: C



Which two code fragments correctly create and initialize a static array of int elements?(Choose two)

A static final int[] a = {100, 200};
B static final int[] a;
static {
a = new int[2];
a[0] = 100;
a[1] = 200;
}
C static final int[] a = new int[2]{100, 200};
D static final int[] a;
static void init(){
a = new int[3];
a[0] = 100;
a[1] = 200;
}


Answer : A B

11	interface DeclareStuff{
12		public static final int EASY = 3;
13		void doStuff(int t);}
14	public class TestDeclare implements DeclareStuff{
15		public static void main(String[] args){
16			int x = 5;
17			new TestDeclare().doStuff(++x);
18		}
19		void doStuff(int s){
20			s += EASY + ++s;
21			System.out.println("S " + s);
22		}
23	}

What is the result?


A s 14
B s 16
C s 10
D Compilation fails
E An exception is thrown at runtime


Answer : B

11	String[] elements = {"for", "tea", "too"};
12	String first = (elements.length > 0)?elements[0]:null;

What is the result?


A Compilation fails
B An exception is thrown at runtime
C The variable first is set to null
D The variable first is set to elements[0].


Answer : D

11	public class ItemTest{
12		private final int id;
13		public ItemTest(int id){ this.id = id;}
14		public void updateId(int newId){id = newId;}
15	
16		public static void main(String[] args){	
17			ItemTest fa = new ItemTest(42);
18			fa.updateId(69);
19			System.out.println(fa.id);
20		}
21	}

What is the result?


A Compilation fails
B An exception is thrown at runtime
C The attribute id in the Item object remains unchanged
D The attribute id in the Item object is modified to the new value
E A new Item object is created with the preferred value in the id attribute


Answer :A

SomeException:

1	public class SomeException{
2	}

Class A:

1	public class A{
2		public void doSomething(){}
3	}

Class B:

1	public class B extends A{
2		public void doSomething(){} throws SomeException;
3	}

Which statement is true about the two classes?

A Compilation of both classes will fail
B Compilation of both classes will succeed
C Compilation of class A will fail. Compilation of class B will succeed
D Compilation of class B will fail. Compilation of class A will succeed



Answer : D



A programmer has an algorithm that requires a java.util.List that privides an
efficient implementation of add(0,object), but does not need to support quick
random access.


what supports these requirements?


A java.util.Queue
B java.util.ArrayList
C java.util.LinearList
D java.util.LinkedList


Answer: D