SCJP程序員認(rèn)證考試章節(jié)練習(xí)(2020.05.29)

1. public class SwitchTest { 
2. public static void main （String []args）  { 
3. System.out.PrintIn（“value =” +switchIt（4））； 
4. } 
5. public static int switchIt（int x）  { 
6. int j = 1； 
7. switch （x） { 
8. case 1： j++； 
9. case 2： j++； 
10. case 3： j++； 
11. case 4： j++； 
12. case 5： j++； 
13. default：j++； 
14. } 
15. return j + x； 
16. } 
17. }    
What is the output from line 3？（）  

public class Foo { 
static int[] a； 
static { a[0]=2； } 
public static void main（ String[] args） {} 
} 
Which exception or error will be thrown when a programmer attempts to run this code？（） 

11. public void someMethod（Object value） { 
12. // check for null value .... 
20. System.out.println（value.getClass（））； 
21. } 
What， inserted at line 12， is the appropriate way to handle a null value？（） 

1. public class SimpleCalc { 
2. public int value； 
3. public void calculate（） { value += 7； } 
4. }
And： 
1. public class MultiCalc extends SimpleCalc { 
2. public void calculate（） { value -= 3； } 
3. public void calculate（int multiplier） { 
4. calculate（）； 
5. super.calculate（）； 
6. value *=multiplier； 
7. } 
8. public static void main（String[] args） { 
9. MultiCalc calculator = new MultiCalc（）； 
10. calculator.calculate（2）； 
11. System.out.println（”Value is： “+ calculator.value）； 
12. } 
13. } 
What is the result？（） 

What is the result？（）

String foo = “blue”；  
 Booleanbar = new Boolean [1]；  
 if （bar[0]） {  
 foo = “green”；  
 }  
What is the result？（）  

Which code fragments will succeed in initializing a two-dimensional array named tab with a size that will cause the expression tab[3][2] to access a valid element？（）  
CODE FRAGMENT a：  int[][] tab = {  { 0， 0， 0 }，  { 0， 0， 0 }  }；  
CODE FRAGMENT b：  int tab[][] = new int[4][]；  for （int i=0； i  
CODE FRAGMENT c：  int tab[][] = {  0， 0， 0， 0，  0， 0， 0， 0，  0， 0， 0， 0，  0， 0， 0， 0  }；  
CODE FRAGMENT d：  int tab[3][2]；  
CODE FRAGMENT e：  int[] tab[] = { {0， 0， 0}， {0， 0， 0}， {0， 0， 0}， {0， 0， 0} }；  

1. import java.util.*； 
2. public class TestSet { 
3. enum Example { ONE， TWO， THREE } 
4. public static void main（String[] args） { 
5. Collection coll = new ArrayList（）； 
6. coll.add（Example.THREE）； 
7. coll.add（Example.THREE）； 
8. coll.add（Example.THREE）； 
9. coll.add（Example.TWO）； 
10. coll.add（Example.TWO）； 
11. coll.add（Example.ONE）； 
12. Set set = new HashSet（coll）； 
13. } 
14. } 
Which statement is true about the set variable on line 12？（） 

Given that Triangle implements Runnable， and：

Which two statements， inserted independently at both lines 35 and 41， tend to allow both threads to temporarily pause and allow the other thread to execute？（）