Java Certification Exam Questions

Write constructor bodies using this() and super() to access overloaded or overriden constructors in the current or a parents class.

    import java.awt.*;
    public class Test() extends Frame {
        public Test(String a) {
          this(a,0);
        }

        public Test( String a, int b) {
          super(a);
          this.b = b;
        }
    }

Employ variables, constructors and methodes for a class, using documentation written standard "Javadoc" format and documentation inherited from a superclass.

    class Super extends Object {
      private float f = 10f;
      protected double g = 0.0;
      public Super() {
        me;
      }
      private me() {
        g=8.0;
      }
    }

    class Sub extends Super {
      public Sub() {
        super();
      }      
      public static void main( String [] args) {
        Super s = new Sub();
        print("g=" + s.g );
      }
    }

Distiguish between overloaded and overriden methods. Identify legal return types for an overloaded method. Identify legal return for overriden method.
overloading=methods with the same name but a different argument list are overloaded.
overridden=methods with the same name and with the same argument list as the super class.
```
    // overloading
    class Car {
      public Car( Color c) {
      }
    }
    class SportsCar extends Car{
      public SportsCar( Color c) {
      }
      public SportsCar( int r, int g, int b) { //overloading the default constructor
      }
    }
```

Demonstrate the use of fields of the class java.awt.Event and identify the affected component, mouse position, and nature and time of the Event.

    public void action( Event e) {
      System.out.println("target= " + e.target); // the affected component
      System.out.println("[x,y]=" + e.x +"," + e.y); // mouse position
      System.out.println("time&nature=" + e.when ); // timestamp
    }

Describe variables of type "array of X" given a type "X". Identify the legal positions for the "{}" part of an array declaration. Construct literal char values using quoted formats. Construct literal char values using the unicode escape format of Java.
```
    public class Test {

      static final char CODE = '\u0a30';

      public static void main( String [] args) {
        int []x[] = new int [10][9];
        float [] g = { 0.5f, 7.1f, 3.1459f };
        char ch = 'c';
      }
    }  
```

Identify all Java keywords from a list of keywords and non-keywords.

    false are: interrupt, const, constant, unsigned, repeat, until
    true are: synchronized, transient, volatile, throws, throw, this, super, try, catch

Define the range of primitive data type byte, short, int, long and char.

    byte    8 bits    (-128)-127
    short   16 bits   (-32768)-32767
    int     32 bits   ()
    long    64 bits   ()

Demonstrate the use of methods of the java.lang.Math class in an assignment expression.

    class Test {
      public static void main( String [] atg ) {
        double x = -1.675;
        System.out.println("abs=" + Math.abs( x ) ); // prints 1.675
        System.out.println("ceil=" + Math.ceil( x ) ); // prints -1.0
        System.out.println("floor=" + Math.floor(x) ); // prints -2.0
        System.out.println("max=" + Math.max( x ,0 ) ); // prints 0
        System.out.println("min=" + Math.min( x, 0 ) ); // prints -1.675
        System.out.println("random= " + Math.random() ); // any thing between 0.0-1.0
        // ..etc
      }
    }
    // NOTE: also asin, acos, atan, and atan2 are valid methods.

Determine the value of a member variable of any type when no explicit assignment has been made to it
Determine the value of an element of an array of any base type, when the array has been constructed but no explicit assignment has been mad to the element. (Knowledge of requirement for definite initialization before use of method automatic variables required)
```
    class Test {
      static int x[] = new int [10];
      int y[] = new int [10];
    }
    // x is initialized, and y!

    class Test2 {
      static int x[];
      int y[];
    }
    // compiles fine but gives NullPointerException, x is not initialized, and y not!
```

Determine the result, in terms of a bit pattern, of applying the >> and the >>> operator to an integer of specified as a bit pattern.

    class Test {
      public static void main( String [] args ) {
        int x = -31;
        int y = x >> 1;  // will give -16
        int z = x >>> 1; // will give 2147483632
        System.out.println( "x= " + x + ", y= " + y + ", z= " + z );
        x = -1;   // NOTE: THIS IS A SPECIAL ONE!!
        y = x >> 1;  // will give -1 
        z = x >>> 1; // will give 2147483647
        System.out.println( "x= " + x + ", y= " + y + ", z= " + z );
      }
    }

Determine at runtime if an object is an instance of a specified class or some subclass of that class using the instanceof operator.

 
    public class Car {

    }

    class SportsCar extends Car {
      public static void main( String [] args ) {
        Car c = new SportsCar();
        Car d = new Car();
        SportsCar e = new SportsCar();
        System.out.print("c=sportscar="); 
        if ( c instanceof SportsCar) { System.out.println("true"); } else { System.out.println("false");  }
        System.out.print("c=car=");  
        if ( c instanceof Car) { System.out.println("true"); } else { System.out.println("false");  }
        System.out.print("d=sportscar=");  
        if ( d instanceof SportsCar) { System.out.println("true"); } else { System.out.println("false");  }
        System.out.print("d=scar=");  
        if ( d instanceof Car) { System.out.println("true"); } else { System.out.println("false");  }
        System.out.print("e=sportscar=");  
        if ( e instanceof SportsCar) { System.out.println("true"); } else { System.out.println("false");  }
        System.out.print("e=scar=");  
        if ( e instanceof Car) { System.out.println("true"); } else { System.out.println("false");  }
      }
    }

Will proof that a: c and e are a both SportsCar and a Car but that d is a Car but not a SportsCar.

Recognize the implications of the immutability rule of the String class Know the link of the unchangeble rule of the String class.
```
    Dunno!!
```

Determine the result of the + operator applied to a combination of variables or constants of any type.

    class TestAgain {
      final int y = 53;
      public static void main( String [] args ) {
        int x = 1;
        double d = 1.652;
        String s = "Andre";
        System.out.println( d + x + "=" + s );      // will do ( d+x ).toString() and will print 2.652
        System.out.println( "" + d + x + "=" + s ); // is different because d.toString() and x.toString() will print 1.6521
        System.out.println( x + s + "=" + d );
        System.out.println( s + x + "=" + d );
      }
    }

Determine tje result of applying the == comparison operator to any two objects of any type. Determine the result of applying the equals() method to any combination of classes java.lang.String, java.lang.Boolean, and java.lang.Object

    class TestIt {
      public static void main( String [] args) {
        String s = "Andre";
        Object o = new String( "Andre" );
        Boolean b = new Boolean( true );

        System.out.print("s==o");  
        if ( s == o ) { System.out.println("true"); } else { System.out.println("false");  }
        System.out.print("s.equals(o)");  
        if ( s.equals(o) ) { System.out.println("true"); } else { System.out.println("false");  }
        o = b;
        System.out.print("b==o");  
        if ( b == o ) { System.out.println("true"); } else { System.out.println("false");  }
        System.out.print("b.equals(o)");  
        if ( b.equals(o) ) { System.out.println("true"); } else { System.out.println("false");  }
      }
    }

Will proof that a: b==o, because the object references are the same (see line o=b;) also s.equals(o)and b.equals(o) because they have the same content. But s!=o because s and o have different object references.

Identify the earliest point in a method at which the object refferred to by a local variable becomes eligible to be garbage collected, in the absence of compiler optimization.
```
      String x = "Andre";
      String y = "y";
      x = "" + x + "y" + y;
      y = null;
```
Distinguish among guaranteed behavior of the garbage collection, finalization mechanisms, and non guearanteed behavior.
```
    Dunno??
```
Write nested loops to iterate blocks with specific values in loop counter variables. (Demonstrate the use of both labeled and unlabeled versions of the break and continue keywords to modify the normal loop.
```
    class Count {
      public static void main( String [] args ) {
        outloop:
        for (int i=0; i <7 ; i++)
          for (int j = 0 ; j < 10) {
            if (i==5)

              break outloop;
          }
        }
      }
    }
```

Write nested conditional code using if or elese and switch constructs. Identify the legal argument types for if(), and switch().

    class Count {
      public static void main( String [] args ) {
        outloop:
        for (int i=0; i <7 ; i++)
          if ( i == 1) {
          } else if ( i == 2) {
          }
          switch (i) {
            case 1: //do
              break;
            case 2: case 3:
              break;
            default:
              break;
          }
        }
      }
    }

Define classes, including member variables an member methods using the modifiers, public, protected or final.

Declare variable using the provate, protected, public, static, final, native or abstract modifiers to those members

Define the accessibility of both variables and methods from other methods in the same or other classes, when the calling method is static or non-static, when the calling method is in the same class as the target, when the calling method is in the subclass of the class containing the target, when the calling method is in the same package as the class containing the target, when no special relationship exists between the calss of the caller and the class of the target, and when the target declaration is qualified by any of the private, protected, public, static, final, or abstract.
```
    Test {
      static int x = 1;
      public int y =1;
      
      Test() {
      }
      public int m1() {
        //
      } 
      static int m2() {
      }
    }

    class A extends Test {
      public static void main( String [] args) {
        A a = new A();
        a.m2();
        int b = a.x;
      }
    }
```

Define the conditions that might prevent a thread from executing

    stop(), suspend(), wait(), sleep(), yield(), destroy()

Write code to create a new Thread. Demonstrate the conditions for a class to implement the interface java.lang.Runnable.

    class Thready extends Thread implements Runnable {
      
      public void run() {
        //
      }

      public static void main( String [] args) {
        Thready t = new Thready();
      }
    }

Write code to start execution of a thread

      Thread t = new Thread();
      (new Thread()).start();
      t.start();

Define the behavior of a thread which invokes the wait() method of an object.

    // it will wait to get notified by notify() or notifyAll()
    public synchronized run() {
      try {
        t.wait();
      } catch (InterruptedException ie) { }
    }

Describe the behavior of a thread, the notify(), and the notifyAll() methods of an Object.
```
    the interaction is handled by the synchronized statement in the method.
```
Describe the interaction between the thread, the wait()????
Write code to implement paint() method of an java.awt.Component class.
```
      Button b = new Button("OK");
      repaint();
```
Describe the interactions between the methods repaint() and update().
```
      repaint======>update(g)=====>paint(g)
```

Describe the appearance, at the handleEvent() and action() methods in the java.awt.Compontent class, of mouse clicks and or keystrokes on each of these components: java.awt.TextField, java.awt.Panel, and java.awt.Canvas.

    TextField t = new TextField(6);
      action = , keystrokes
      handleEvent = mouse clicks, keystrokes
    Panel p = new Panel();
      action = keystrokes
      handleEvent = mouse events
    Canvas p = new Canvas(); 
      handleEvent = mouse events

Describe the significance of a column where one of these components is using a proportional font or a fixed font.

Construct a java.awt.TextArea or java.awt.TextField that prefers to display a specific number of columns

    // 30 columns,
    TextField s = new TextField(30);
    TextArea ta = new TextArea( 4, 30); // row, columns

Construct an HTML Applet tag to embed an applet in a Web page. Control the width and height of the applet. Supply named parameter values to the applet. Write code in an applet that reads the value of the named parameter specified in the applet tag.
```
    <applet code=my.class width=100 height=100>
    <param name=1 value="Andre">
    </applet>

    // javacode
    String andre = getParameter("1");
```

Demonstrate the use of methods

show(), hide(), enable(), 
                  disable(), size(), setForeground()

and setBackground for a java.awt.Component class.

    Frame f = new Frame("My Frame");
    f.resize(100,100);
    if ( f.size().width == 100) {
      f.setForeground( Color.red );
      f.setBackground( Color.orange );
      Button b;
      f.add( b = new Button() );
      f.show();
      b.disable();
    }
    else {
      f.hide();
    }

Demonstrate the use of the methods add( Component) and add( String, Component) of the java.awt.Container.
```
    add( "Center", new Button() ); // BorderLayout()
    add( new Button() ); // FlowLayout()
```

List the displayable classes in the java.awt package that are valid arguments to these methods and those which are not valid.

  valid are:  Container, Component, Frame, Canvas, Button, TextField, TextArea, 
              Scrollbar, List, Choice, Checkbox, Window, Panel,
  not valid are: Menu, MenuItem, Event

Distinguish between WAWT classes which are directly responsible for determining component layout and those which are responsible for implementing that layout.
```
    component layout: LayoutManager, 
    implementation: BorderLayout, FlowLayout, GridLayout, GridBagLayout
```
Change the layout scheme associated with the AWT container. Describe the effect of invoking overridden methods in base and derived classes.
```
    Panel p = new Panel();
    p.setLayout( new BorderLayout() );
    // second part of the question???
```
Define which expressions are excluded, and their resulting values in compound expressions involving the operators &, |, && and ||.
```
    5 | 2 = 7
    5 || 2 = true/false
    5 & 2 = 0
    5 & 2 = true/false
```
Identify the effect of assignment and modifying operations upon objects, reference variables, and primitive variables.
```
    Object s = new String("Andre");
    String b = s;
```
Describe the output from a program performing these operations by studying the source.
class TestIt { public static void main( String [] args) { String s = "Andre"; Object o = new String( "Andre" ); Boolean b = new Boolean( true ); System.out.print("s==o"); if ( s == o ) { System.out.println("true"); } else { System.out.println("false"); } System.out.print("s.equals(o)"); if ( s.equals(o) ) { System.out.println("true"); } else { System.out.println("false"); } o = b; System.out.print("b==o"); if ( b == o ) { System.out.println("true"); } else { System.out.println("false"); } System.out.print("b.equals(o)"); if ( b.equals(o) ) { System.out.println("true"); } else { System.out.println("false"); } } }

Write code to create and throw an Exception given a specified test that returns true

    public boolean test() {
      try {
        if ( a < b ) 
          throw new Exception();
      } catch (Exception e) { }
    }

Write the correct method declaration to support this behavior.

    public boolean test() throws Exception {
      if ( a < b ) 
        throw new Exception();
    }

Describe the prototye of the default constructor.

    the default constructor is invoked when there is other constructor.

List the circumstances under which the default constructor is created and the circumstances which inhibit implicit creation of a default constructor.

    // normally
    public class Test extends Object {
        public Test( int a ) {
          bee = a;
        }
        public Test() { //default constructor
          bee = 0;
        }
    }

    // implicitly
    public class Test extends Obect {

      public static void main(String at[]) {
        Test t = new Test();
      }
    }

Evaluate statements regarding thread scheduling
```
    ?What is scheduling? setPriority??
```

Write code to create a new Thread of execution, using both Runnable interface and the Thread class

      class Test implements Runnable {
        Thread t;
        void start() {   t = new Thread(); }
        void stop() {  t= null; }
        void run() { //do somthing }
        public static void main( String [] args ) {
          Test t = new Test();
          t.start();
        }
      }

Demonstrate the use of the synchronized keyword to require a thread of execution to obtain an object lock prior to proceeding.

    // it will wait to get notified by notify() or notifyAll()
    public void run() {
      try {
        t.wait();
      } catch (InterruptedException ie) { }
    }

Identy the return value of an overridden

handleEvent() 
                  or action()

method to control propagation of the event up the container hierarchy.

    return true = event is handled by the component do push it to the parent component class
    return false = event is not handled so push it to the parent component class

Select from a list valid reasons why an event might be passed up a container hierarchy.

    we just want react on a specific mouse event , but the rest we dont want to implement so
    we pass it on the container hierarchy which has defaults to handle these events.

Select from a list given descriptions using

BorderLayout, 
                  FlowLayout

, and GridLayout.

    FlowLayout: default add and resizes the components to the container in rows.
    BorderLayout: has 5 ways N, E, W, S and Center to put layouts
    GridLayout: is a cell structure.

Select from a lost strategies to achieve a dynamic resizing of a Component in the horizonal, vertical, both or neither directions.
```
    FlowLayout
```

Select from a list all the operators which are legal in String expressions.

    valid are: length(), substring(), trim(), toLowerCase(), toUpperCase(), charAt() etc..

Demonstrate the use of the following String methods: length(), toUpperCase(), toLowerCase(), equals(), equalsIgnoreCase(), charAt(), concat(), indexOf(), lastIndexOf(), substring(), toString() and trim().
```
    // the most unusual
    String a = "Andre"
    String b = "andre"
    b.equalsIgnoreCase( a); // true
    b = b.concat(a); // "andreAndre"
```

{submenus}

DISCLAIMER

More is added to the list, but what I realy need is your help to keep this information up-to-date and may be it needs correcting in one way or the other. Please feel free to help me complement these question and answers drop us an email at this address.