SCJP考试题310-025(第二套<4>)92-147/147

310-025
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QUESTION NO: 92
Given:
1. String foo = “blue”;
2. Boolean[]bar = new Boolean [1];
3. if (bar[0]) {
4. foo = “green”;
5. }
What is the result?
A. Foo has the value of “”
B. Foo has the value of null.
C. Foo has the value of “blue”
D. Foo has the value of “green”
E. An exception is thrown.
F. The code will not compile.
Answer: F （错的？）

public class x {
   public static void main(String [] args) {
       String foo = "blue";
       Boolean[]bar = new Boolean [1];
       if (bar[0]) {
       foo = "green";
       }
       System.out.println("foo = " + foo);
   }
}/** Output:
Exception in thread "main" java.lang.NullPointerException
    at x.main(x.java:5)
*/ 

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QUESTION NO: 93

Exhibit:
1. public class X {
2. public static void main (String[]args) {
3. String s1 = new String (“true”);
4. Boolean b1 = new Boolean (true);
5. if (s2.equals(b1)) {
6. System.out.printIn(“Equal”);
7. }
8. }
9. }
What is the result?
A. The program runs and prints nothing.
B. The program runs and prints “Equal”
C. An error at line 5 causes compilation to fail.
D. The program runs but aborts with an exception.
Answer: A

public class X {
 public static void main (String[]args) {
 String s1 = new String ("true");
 Boolean b1 = new Boolean (true);
 System.out.println("b1 is String: " + checkType(b1));
 if (s1.equals(b1)) {
 System.out.println("Equal");
 }
}
  static boolean checkType(Object obj){
     return (obj instanceof String);
 }
}

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QUESTION NO: 94
Given:
1. public class Foo {
2. public static void main (String []args) {
3. int i = 1;
4. int j = i++;
5. if ((i>++j) && (i++ ==j)) {
6. i +=j;
7. }
8. }
9. }
What is the final value of i?
A. 1
B. 2
C. 3
D. 4
E. 5
Answer: B

public class X {
    public static void main(String[] args) {
        int i = 1;
        int j = i++;
        if ((i > ++j) && (i++ == j)) {
            i += j;
        }
        System.out.print(i);
    }
}//Output: 2

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QUESTION NO: 95
Exhibit:
1. public class X {
2. public static void main (String[]args) {
3. string s = new string (“Hello”);
4. modify(s);
5. System.out.printIn(s);
6. }
7.
8. public static void modify (String s) {
9. s += “world!”;
10. }
11. }
What is the result?
E. The program runs and prints “Hello”
F. An error causes compilation to fail.
G. The program runs and prints “Hello world!”
H. The program runs but aborts with an exception.
Answer: A

public class X {
    public static void main(String[] args) {
        String s = new String("Hello");
        modify(s);
        s += "world!";
        System.out.println(s);
    }

    public static void modify(String s) {
        s += "world!";
    }
}

String对象是不可变的。

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QUESTION NO: 96
Which two are equivalent? (Choose Two)
A. 16>4
B. 16/2
C. 16*4
D. 16>>2
E. 16/2^2
F. 16>>>2
Answer: D, F

>>> 右移，高位补零； >> 右移，高位补和原符号为相同的数。

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QUESTION NO: 97
Exhibit:
1. public class X {
2. public static void main (String[]args) {
3. int [] a = new int [1]
4. modify(a);
5. System.out.printIn(a[0]);
6. }
7.
8. public static void modify (int[] a) {
9. a[0] ++;
10. }
11. }
What is the result?
A. The program runs and prints “0”
B. The program runs and prints “1”
C. The program runs but aborts with an exception.
D. An error “possible undefined variable” at line 4 causes compilation to fail.
E. An error “possible undefined variable” at line 9 causes compilation to fail.
Answer: B

public class X {
    public static void main(String[] args) {
        int[] a = new int[1];
        modify(a);
        System.out.println(a[0]);
    }

    public static void modify(int[] a) {
        a[0]++;
    }
}//Output: 1

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QUESTION NO: 98
Given:
13. public class Foo {
14. public static void main (String [] args) {
15. StringBuffer a = new StringBuffer (“A”);
16. StringBuffer b = new StringBuffer (“B”);
17. operate (a,b);
18. system.out.printIn{a + “,” +b};
19. )
20. static void operate (StringBuffer x, StringBuffer y) {
21. y.append {x};
22. y = x;
23. )
24. }
What is the result?
A. The code compiles and prints “A,B”.
B. The code compiles and prints “A, BA”.
C. The code compiles and prints “AB, B”.
D. The code compiles and prints “AB, AB”.
E. The code compiles and prints “BA, BA”.
F. The code does not compile because “+” cannot be overloaded for stringBuffer.
Answer: B

public class X {
    public static void main(String[] args) {
        StringBuffer a = new StringBuffer("A");
        StringBuffer b = new StringBuffer("B");
        operate(a, b);
        System.out.println(a + "," + b);
    }

    static void operate(StringBuffer x, StringBuffer y) {
        y.append(x);
        y = x;
    }
}

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QUESTION NO: 99
Given:
1. public class X {
2. public static void main (String[] args) {
3. byte b = 127;
4. byte c = 126;
5. byte d = b + c;
6. }
7. }
Which statement is true?
A. Compilation succeeds and d takes the value 253.
B. Line 5 contains an error that prevents compilation.
C. Line 5 throws an exception indicating “Out of range”
D. Line 3 and 4 contain error that prevent compilation.
E. The compilation succeeds and d takes the value of 1.
Answer: B

public class X {
 public static void main (String[] args) {
 byte b = 127;
 byte c = 126;
// byte d = b + c; //Type mismatch: cannot convert from int to byte
}
}

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QUESTION NO: 100
Given:
1. public class WhileFoo {
2. public static void main (String []args) {
3. int x= 1, y = 6;
4. while (y--) {x--;}
5. system.out.printIn(“x=” + x “y =” + y);
6. }
7. }
What is the result?
A. The output is x = 6 y = 0
B. The output is x = 7 y = 0
C. The output is x = 6 y = -1
D. The output is x = 7 y = -1
E. Compilation will fail.
Answer: E

public class X {
    public static void main(String[] args) {
        int x = 1, y = 6;
//        while (y--) {//Type mismatch: cannot convert from int to boolean
//            x--;
//        }
        System.out.println("x=" + x + "y =" + y);
    }
}

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QUESTION NO: 101
Which statement is true?
A. The Error class is a untimeException.
B. No exceptions are subclasses of Error.
C. Any statement that may throw an Error must be enclosed in a try block.
D. Any statement that may throw an Exception must be enclosed in a try block.
E. Any statement that may thro a runtimeException must be enclosed in a try block.
Answer: D
QUESTION NO: 102
Exhibit:
1. int I=1, j=0
2.
3. switch(i) {
4. case 2:
5. j+=6;
6.
7. case 4:
8. j+=1;
9.
10. default:
11. j +=2;
12.
13. case 0:
14. j +=4;
15. }
16.
What is the value of j at line 16?
A. 0
B. 1
C. 2
D. 4
E. 6
Answer: AE