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详细介绍scjp考试指南包括基础语法和文件读取

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 5.     public static void main(String[] args) {
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 6.        System.out.println(str1);
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 7.     }
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10.     public static void main(int[] args) {
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11.       System.out.println(str2); 
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12.     }               
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13.   }
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a.   Duplicate method main(), compilation error at line 5.
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b.   Duplicate method main(), compilation error at line 10. 
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c.   Prints "main method with String[] args".  
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d.   Prints "main method with int[] args".
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Q10
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In the following applet, how many buttons will be displayed?
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 1.    import java.applet.*;
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 2.    import java.awt.*;
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 3.    public class Q16 extends Applet {
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 4.      Button okButton = new Button("Ok");
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 5.      public void init() {
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 6.        add(okButton);
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 7.        add(okButton);
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 8.        add(okButton);     
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 9.        add(okButton);     
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10.        add(new Button("Cancel"));     
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14.        add(new Button("Cancel"));
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15.        add(new Button("Cancel"));     
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16.        add(new Button("Cancel"));     
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18.        setSize(300,300);     
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19.      }
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20.    } 
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a.  1 Button with label "Ok" and 1 Button with label "Cancel".
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b.  1 Button with label "Ok" and 4 Buttons with label "Cancel".
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c.  4 Buttons with label "Ok" and 1 Button with label "Cancel".
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d.  4 Buttons with label "Ok" and 4 Buttons with label "Cancel".
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Q11
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What is the output of the following program?
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 1.    class Test {
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 2.      void show() {      
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 3.         System.out.println("non-static method in Test");
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 4.      }
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 5.    }
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 6.    public class Q3 extends Test {
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 7.      static void show() {
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 8.         System.out.println("Overridden non-static method in Q3");
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 9.      }
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10.      public static void main(String[] args) {
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11.         Q3 a = new Q3();
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12.      }
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13     }
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a.   Compilation error at line 2. 
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b.   Compilation error at line 7. 
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c.   No compilation error, but runtime exception at line 2.
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d.   No compilation error, but runtime exception at line 7.
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Q12
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What will happen if you compile/run the following code?
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 1.   public class Q21 {
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 2.      int maxElements; 
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 3.      void Q21() {      
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 4.        maxElements = 100;
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 5.        System.out.println(maxElements); 
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 6.      }     
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 7.      Q21(int i) {
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 8.        maxElements = i;
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 9.        System.out.println(maxElements);          
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10.      }     
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11.      public static void main(String[] args) {
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12.        Q21 a = new Q21();
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13.        Q21 b = new Q21(999);
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14.    
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15.      }
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16.   }             
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a.   Prints 100 and 999.
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b.   Prints 999 and 100.
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c.   Compilation error at line 2, variable maxElements was not initialized.
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d.   Compilation error at line 12.
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Q13
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Given the following class definition, which of the following methods could be legally placed after the comment //Here
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1.   public class Rid {
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2.      public void amethod(int i, String s){}
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3.      //Here
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4.   }
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a.   public void amethod(String s, int i) {}
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b.   public int  amethod(int i, String s) {} 
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c.   public void amethod(int i, String mystring) {} 
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d.   public void Amethod(int i, String s) {}
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Q14
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Given the following class definition, which of the following statements would be legal after the comment //Here
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 1.    class InOut {
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 2.       String s= new String("Between");
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 3.       public void amethod(final int iArgs) {
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 4.          int iam;
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 5.          class Bicycle{
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 6.              public void sayHello(){
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 7.                    //Here
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 8.                } //End of bicycle class
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 9.          }
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10.       } //End of amethod
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11.       public void another(){
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12.        int iOther;
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13.       }
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14.    }
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a. System.out.println(s); 
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b. System.out.println(iOther);
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c. System.out.println(iam);
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d. System.out.println(iArgs);
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Q15
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Which of the following methods are members of the Vector class and allow you to input a new element
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a. addElement()
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b. insert()
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c. append()
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d. addItem()
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Q16
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What will happen when we try to compile the following code.
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 1.   public void WhichArray( Object x ) {
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 2.     if( x instanceof int[] ) {
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 3.       int[] n = (int[]) x ;
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 4.       for( int i = 0 ; i < n.length ; i++ ){
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 5.         System.out.println("integers = " + n[i] );
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 6.       }
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 7.     }    
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 8.     if( x instanceof String[] ) {
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 9.       System.out.println("Array of Strings");
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10.    }
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11.   }
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a. The compiler objects to line 2 comparing an Object with an array.
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b. The compiler objects to line 3 casting an Object to an array of int primitives.
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c. The compiler objects to line 7 comparing an Object to an array of Objects.
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d. It compiles without error.
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Q17
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Consider the following class
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 1.   class Tester {
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 2.      void test (int i)    { System.out.println ("int version"); }
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 3.      void test (String s) { System.out.println ("String version"); } 
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 4. 
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 5.      public static void main (String args[]) {
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 6.        Tester c = new Tester ();
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 7.        char ch = 'p'; 
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 8.        c.test (ch);
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 9.      }
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10.   }
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Which of the following statements below is true?(Choose one.)
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a. Line 3 will not compile, because void methods cannot be overridden.
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b. Line 8 will not compile, because there is no conversion of test() that takes a char argument.        
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c. The code will compile and produce the follwing output "int version"
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d. The code will compile and produce the follwing output "String version" 
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Q18
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You are creating a ToolBase class which will be extended by other programmers. The ToolBase class contains a single abstract method, createTool.
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Which of the following statements are true?
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a. The ToolBase class must be declared abstract.
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b. Classes extending ToolBase must not be declared abstract.
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c. The ToolBase class must not be declared final.
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d. The following variable declaration is illegal in any context "ToolBase myTB;"
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Q19
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Given the following hierarchical relationship of several classes.
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 1. Object
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 2.  |---TypeA
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 3.  |     |-----TypeAB
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 4.  |     |-----TypeAC
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 5.  |--------TypeY
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And given the following method definition
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 6.   public sayType(Object x ){
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 7.     if(x instanceof Object )System.out.print("Object,");
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 8.     if(x instanceof TypeA  )System.out.print("TypeA,");
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 9.     if(x instanceof TypeAB )System.out.print("TypeAB,");
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10.     if(x instanceof TypeAC )System.out.print("TypeAC,");
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11.   }
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What would the program output be if the following line was executed
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12.   sayType( new TypeAB() );
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a. Object,
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b. Object,TypeA,TypeAB,
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c. TypeAB,
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d. Object,TypeAC,
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Q20
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What happens on trying to compile and run the following code?
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1.   public class EqualsTest{
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2.     public static void main(String args[]){
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3.       Long LA = new Long( 9 ) ;
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4.       Long LB = new Long( 9 ) ;
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5.       if( LA == LB ) System.out.println("Equal");
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6.       else System.out.println("Not Equal");
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7.     }
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8.   }
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a. The program compiles but throws a runtime exception in line 5.
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b. The program compiles and prints "Not Equal".
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c. The program compiles and prints "Equal".
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d. The program throws compilation error.
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Q21
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Which one statement in true about the application below?
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1.   class StaticStuff {
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2.     static int x = 10;
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3.     static { x += 5; }
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4.     public static void main(String args[]) {
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5.       System.out.println("x = " + x);
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6.     }
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7.     static { x /= 5; }
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8.   }
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a. The code compiles, and execution produces the output x = 10.
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b. The code compiles, and execution produces the output x = 15.
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c. The code compiles, and execution produces the output x = 3.           
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d. Line 7 will not compile, because you can have only one static initializer.
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Q22
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Assume the the class AcLis implements the ActionListener interface. The code fragment below constructs a button ande gives it four action listeners. When the button is pressed, which action listener is the first to get its actionPerformed() method invoked?
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 1.   Button btn = new Button("Hello");
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 2.   AcLis a1 = new AcLis();
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 3.   AcLis a2 = new AcLis(); 
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 4.   AcLis a3 = new AcLis();
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 5.   btn.addActionListener(a1);
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 6.   btn.addActionListener(a2);
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 7.   btn.addActionListener(a3);
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 8.   btn.removeActionListener(a2);
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 9.   btn.removeActionListener(a3);
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10.   btn.addActionListener(a3);
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11.   btn.addActionListener(a2);
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a. a1 gets its actionPerformed() method invoked first.
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b. a2 gets its actionPerformed() method invoked first.
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c. a3 gets its actionPerformed() method invoked first.
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d. It is impossible to know which listener will be first.
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Q23
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Which statement or statements are true about the code listed below?
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1.   public class MyTextArea extends TextArea  {
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2.     public MyTextArea(int nrows, int ncols) {
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3.       enableEvents(AWTEvent.TEXT_EVENT_MASK);
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4.     }
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5.     public void processTextEvent(TextEvent te) {
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6.       System.out.println("Processing a text event");
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7.     }
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8.   }
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a. The source code must appear in a file called MyTextArea.java.
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b. Between lines 2 and 3, a call should be made to super(nrows,ncols) so that the next component will have the correct size.
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c. Between lines 6 and 7, the following code should appear "return true;"
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d. Between lines 6 and 7, the following code should appear "super.processTextEvent(te);"
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Q24
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Which statement or statements are true about the code fragment listed below? (HINT The ActionListener and ItemListener interface each define a single method.)
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1.   class MyListener implements ActionListener, ItemListener {
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2.     public void actionPerformed(ActionEvent e) {
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3.       System.out.println("Action.");