Which is valid in a class that extends class A?

class A 
{  
    protected int method1(int a, int b) 
    {
        return 0; 
    } 
}

If a Runnable object is passed to the Thread constructor, then the run method of the Thread class will invoke the run method of the Runnable object.

In this case, however, the run method in the Thread class is overridden by the run method in MyThread class. Therefore the run() method in MyRunnable is never invoked.

Both times, the run() method in MyThread is invoked instead.

Option A is correct. The assertion status can be set for a named top-level class and any nested classes contained therein. This setting takes precedence over the class loader's default assertion status, and over any applicable per-package default. If the named class is not a top-level class, the change of status will have no effect on the actual assertion status of any class.

Option B is wrong. Is there such a thing as conditional compilation in Java?

Option C is wrong. For private methods - yes. But do not use assertions to check the parameters of a public method. An assert is inappropriate in public methods because the method guarantees that it will always enforce the argument checks. A public method must check its arguments whether or not assertions are enabled. Further, the assert construct does not throw an exception of the specified type. It can throw only an AssertionError.

Option D is wrong. Because you're never supposed to handle an assertion failure. That means don't catch it with a catch clause and attempt to recover.

In the fix() method, the reference variable tt refers to the same object (class Two) as the t reference variable. Updating tt.x in the fix() method updates t.x (they are one in the same object). Remember also that the instance variable x in the Two class is initialized to 0.

Access modifiers dictate which classes, not which instances, may access features.

Methods and variables are collectively known as members. Method and variable members are given access control in exactly the same way.

private makes a member accessible only from within its own class

protected makes a member accessible only to classes in the same package or subclass of the class

default access is very similar to protected (make sure you spot the difference) default access makes a member accessible only to classes in the same package.

public means that all other classes regardless of the package that they belong to, can access the member (assuming the class itself is visible)

final makes it impossible to extend a class, when applied to a method it prevents a method from being overridden in a subclass, when applied to a variable it makes it impossible to reinitialise a variable once it has been initialised

abstract declares a method that has not been implemented.

transient indicates that a variable is not part of the persistent state of an object.

volatile indicates that a thread must reconcile its working copy of the field with the master copy every time it accesses the variable.

After examining the above it should be obvious that the access modifier that provides the most restrictions for methods to be accessed from the subclasses of the class from another package is C - protected. A is also a contender but C is more restrictive, B would be the answer if the constraint was the "same package" instead of "any package" in other words the subclasses clause in the question eliminates default.

The main() method properly catches and handles the RuntimeException in the catch block, finally runs (as it always does), and then the code returns to normal.

A, B and C are incorrect based on the program logic described above. Remember that properly handled exceptions do not cause the program to stop executing.

Option A is correct because it is sometimes advisable to thrown an assertion error even if assertions have been disabled.

Option B is incorrect because it is considered appropriate to check argument values in private methods using assertions.

Option C is incorrect; finally is never bypassed.

Option D is incorrect because AssertionErrors should never be handled.

Option A is correct. notify() - wakes up a single thread that is waiting on this object's monitor.

Option B is wrong. wait() causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.

Option C is wrong. Methods of the InputStream class block until input data is available, the end of the stream is detected, or an exception is thrown. Blocking means that a thread may stop until certain conditions are met.

Option D is wrong. sleep() - Causes the currently executing thread to sleep (temporarily cease execution) for a specified number of milliseconds. The thread does not lose ownership of any monitors.

A boolean can only be assigned the literal true or false.

String objects are immutable, they cannot be changed, in this case we are talking about the replace method which returns a new String object resulting from replacing all occurrences of oldChar in this string with newChar.

b.replace(char oldChar, char newChar);

But since this is only a temporary String it must either be put to use straight away i.e.

System.out.println(b.replace('a','d'));

Or a new variable must be assigned its value i.e.

String c = b.replace('a','d');

This question is about the + (plus) operator and the overriden + (string cocatanation) operator. The rules that apply when you have a mixed expression of numbers and strings are:

If either operand is a String, the + operator concatenates the operands.

If both operands are numeric, the + operator adds the operands.

The expression on line 6 above can be read as "Add the values i1 and i2 together, then take the sum and convert it to a string and concatenate it with the String from the variable s1". In code, the compiler probably interprets the expression on line 8 above as:

System.out.println( new StringBuffer() 
    .append(new Integer(i1 + i2).toString()) 
    .append(s1) 
    .toString() );