SCJP认证试题(七)

 /**
 *
 * @author yaoyuan
 */
11	public static int sum(List list){
12		int sum = 0;
13		for(Iterator iter = list.iterator();iter.hasNext();){
14			int I = ((Integer)iter.next()).intValue();
15			sun += I;
16		}
17		return sum;
18	}

/**
*Which three changes must be made to the method sum to use generics?(choose three)
*
*
*A remove line 14
*B replace line 14 with "int I=iter.next()"
*C replace line 13 with "for(int I:intList)"
*D replace line 13 with "for(Iterator iter : intList)"
*E replace the method declaration with "sum(List<int>intList)"
*F replace the method declaration with "sum(List<Integer>intList)"
*/

// Answer : A C F

 /**
 *
 * @author yaoyuan
 */

23	Object[] myObjects = {
24		new Integer(12), 
25		new String("foo"), 
26		new Integer(5), 
27		new Boolean(true)
28	}
29	Arrays.sort(myObjects);
30	for(int i=0;i<myObjects.length;i++){
31		System.out.print(myObjects[i].toString());
32		System.out.print(" ");
33	}

/**
*What is the result?
*
*
*A Compilation fails due to an error in line 23
*B Compilation fails due to an error in line 29
*C A ClassCaseException occurs in line 29
*D A ClassCaseException occurs in line 31
*E The value of all four object prints in natural order
*/

// Answer : C

/**
 *
 * @author yaoyuan
 */

import java.util.*;

public class PQ{
	public static void main(String[] args){
		PriorityQueue<String> pq = new PriorityQueue<String>();
		pq.add("carrot");
		pq.add("apple");
		pq.add("banana");
		System.out.println(pq.poll() + ":" + pq.peek());
	}
}

/**
*which code,inserted ay line 14,will allow this class to correctly serialized
*and desterilize?
*
*A apple:apple
*B carrot:apple
*C apple:banana
*D banana:apple
*E carrot:carrot
*F carrot:banana
*/

// Answer : C

/** API 详解
一个基于优先级堆的无界优先级队列。优先级队列的元素按照其自然顺序进行排序，或者根据构造队列时提供的 Comparator 进行排序，具体取决于所使用的构造方法。优先级队列不允许使用 null 元素。依靠自然顺序的优先级队列还不允许插入不可比较的对象（这样做可能导致 ClassCastException）。
*/

 /**
 *
 * @author yaoyuan
 */

11	public class Key{
12		private long id1;
13		private long id2;
14	
15		//class key methods
16	}

/**
*A programmer is developing a class Key, that will be used as a key in a standard java.util.HashMap.
*Which two methods should be overridden to assure that key works correctly as a key?(choose two)
*
*
*
*A public int hashCode()
*B public Boolean equals(Key k)
*C public int compareTo(Object o)
*D public Boolean equals(Object o)
*/

// Answer : A D

 /**
 *
 * @author yaoyuan
 */

//	insert code here
	private N min, max;
	public N getMin(){return min;}
	public N getMax(){return max;}
	public void add(N added){
		if(min == null || added.doubleValue() < min.doubleValue())
			min = added;
		if(max == null || added.doubleValue() < max.doubleValue())
			max = added;
	}
}

/**
*Which two ,inserted will allow the code to compile?(choose two)
*
*
*A      public class M inMax<?>{
*B public class M inMax<? extends Number>{
*C public class M inMax<N extends Object>{
*D public class M inMax<N extends Number>{
*E public class M inMax<? extends Object>{
*F public class M inMax<N extends Integer>{
*/

// Answer : D F



/**
*
* @author yaoyuan
*/

enum Example{ONE, TWO, THREE}

/**
*Which statement is true?
*
*A      The expressions(ONE == ONE) and ONE.equals(ONE) are both guaranteed to be true
*B The expression(ONE == TWO) is guaranteed to be true and ONE compare to (TWO) is guaranteed to be * less than one
*C The Example values cannot be used in a raw java.util.HashMap;instead, the programmer must use a * java.util.EnumMap
*D The Example values can be used in a java.util.SortedSet, but the set will not be sorted because * enum erated Type do not implement java.lang.Comparable
*/

// Answer : A

 /**
 *
 * @author yaoyuan
 */

11	public void getNumbers(){
12		ArrayList numbers = new ArrayList();
13		for(int i=0;i<10;i++){
14			int value = i * ((int)Math.random());
15			Integer intObj = new Integer(value);
16			numbers.add(intObj);
17		}
18		System.out.println(numbers);
19	}

/**
*Which line of code marks the earliest point that an object referenced by intObj becomes a candidate for
*garbage collection?
*
*
*A line 16
*B line 17
*C line 18
*D line 19
*E The object is not a candidate for garbage collection
*/

// Answer : D

 /**
 *
 * @author yaoyuan
 */

12	public class Yippee2{
13
14		public static void main(String[] args){
15			for(int x =1;x < yahoo.length;x++){
16				System.out.print(yahoo[x] + " ");
17			}
18		}
19	}

/**
*the command and line invocation : java Yippee2 a b c
*What is the result?
*
*A a b
*B b c
*C a b c
*D Compilation fails
*E An exception is thrown at runtime
*/

// Answer : B

 /**
 *
 * @author yaoyuan
 */

10	class Inner{
11		private int x;
12		public void setX(int x){this.x=x;}
13		public int getX(){return x;}
14	}
15	
16	class Outer{
17		private Inner y;
18		public void setY(Inner y){this.y=y;}
19		public Inner getY(){return y;}
20	}
21	
22	public class Gamma{
23		public static void main(String[] args){
24			Outer o = new Outer();
25			Inner i = new Inner();
26			int n = 10;
27			i.setX(n);
28			o.setY(i);
29			//insert code here
30			System.out.println(o.getY().getX());
31		}
32	}	

/**
*Which three code fragments, added individually at line 29, produce the output 100?
*(choose three)
*
*
*A      n = 100;
*B i.setY(100);
*C o.getY().setX(100);
*D i = new Inner(); i.setX(100);
*E o.setY(i); i = new Inner(); i.setX(100);
*F i = new Inner();i.setX(100); o.setY(i);
*/

// Answer : B C F

 /**
 *
 * @author yaoyuan
 */
1	package utils;
2	
3	public class Repetition{
4		public static String twice(String s){return s+s;}
5	}
/*
*and given another class Demo:
*/
1	//insert code here
2	
3	public class Demo{
4		public static void main(String[] args){
5			System.out.println(twice("pizza"));
6		}
7	}

/**
*Which code should be inserted at line 1 of Demo.java to compile and run Demo to print"pizzapizza"
*
*
*A      import utils.*;
*B static import utils.*;
*C import utils.Repetition.*;
*D static import utils.Repetition.*;
*E import utils.Repetition.twice();
*F import static utils.Repetition.twice;
*G import import utils.Repetition.twice;
*/

// Answer : F