CLASSES

Examples of Method Declarations

8.4.8

pos = 0;

}

}

class LineBufferOutput extends BufferOutput {

LineBufferOutput(OutputStream o) { super(o); }

public void putchar(char c) throws IOException {

super.putchar(c);

if (c ==  \n )

flush();

}

}

class Test {

public static void main(String[] args)

throws IOException

{

LineBufferOutput lbo =

new LineBufferOutput(System.out);

lbo.putstr("lbo\nlbo");

System.out.print("print\n");

lbo.putstr("\n");

}

}

This example produces the output:

lbo

print

lbo

The class

BufferOutput

 implements a very simple buffered version of an

OutputStream

, flushing the output when the buffer is full or

flush

 is invoked.

The subclass

LineBufferOutput

 declares only a constructor and a single method

putchar

, which overrides the method

putchar

 of

BufferOutput

. It inherits the

methods

putstr

 and

flush

 from class

Buffer

.

In the

putchar

 method of a

LineBufferOutput

 object, if the character argu 

ment is a newline, then it invokes the

flush

 method. The critical point about over 

riding in this example is that the method

putstr

, which is declared in class

BufferOutput

, invokes the

putchar

 method defined by the current object

this

,

which is not necessarily the

putchar

 method declared in class

BufferOutput

.

Thus, when

putstr

 is invoked in

main

 using the

LineBufferOutput

 object

lbo

, the invocation of

putchar

 in the body of the

putstr

 method is an invocation

of the

putchar

 of the object

lbo

, the overriding declaration of

putchar

 that

checks for a newline. This allows a subclass of

BufferOutput

 to change the

behavior of the

putstr

 method without redefining it.

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