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&nbsp;&nbsp;('extends' InterfaceName (',' InterfaceName)*)?<BR>
&nbsp;&nbsp;'{' FieldDeclaration* '}'<BR>
;</TT>
</BLOCKQUOTE>
<P>
Interface declarations are similar to classes. The main difference
between them is that interface declarations can extend one or
more existing interfaces.
<BLOCKQUOTE>
<TT>FieldDeclaration =<BR>
&nbsp;&nbsp;DocComment? MethodDeclaration<BR>
| DocComment? ConstructorDeclaration<BR>
| DocComment? VarableDeclaration<BR>
| StaticInitializer<BR>
| ';'<BR>
;</TT>
</BLOCKQUOTE>
<P>
DocComment is an undefined terminal. It takes the form of a multiline
comment beginning with <TT>/**</TT>
and ending with the standard <TT>*/</TT>.
<BLOCKQUOTE>
<TT>MethodDeclaration =<BR>
&nbsp;&nbsp;Modifier* Type Identifier '(' ParameterList? ')' (
'[' ']' )*<BR>
&nbsp;&nbsp;( '{' Statement* '}' | ';' )<BR>
;</TT>
</BLOCKQUOTE>
<P>
Grammars enable syntactic constructs that cause the compiler to
issue semantic errors. Notice that the body of a method is optional.
Syntactically, this is correct. Semantically, however, this is
correct only if a native or abstract modifier is present.
<BLOCKQUOTE>
<TT>ConstructorDeclaration =<BR>
&nbsp;&nbsp;Modifier* Identifier '(' ParameterList? ')'<BR>
&nbsp;&nbsp;'{' Statement* '}'<BR>
;<BR>
VariableDeclaration =<BR>
&nbsp;&nbsp;Modifier* Type VariableDeclarator (',' VariableDeclarator)*
';'<BR>
;<BR>
VariableDeclarator =<BR>
&nbsp;&nbsp;Identifier ('[' ']')* ('=' VariableInitializer)?<BR>
;</TT>
</BLOCKQUOTE>
<P>
A variable declarator may specify an array: <TT>int
name[]</TT>. It also is legal for a Type to specify an
array: <TT>int[] name</TT>. Either
form is correct.
<BLOCKQUOTE>
<TT>VariableInitializer =<BR>
&nbsp;&nbsp;Expression<BR>
| '{' (VariableInitializer ( ',' VariableInitializer )* ','? )?
'}'<BR>
;</TT>
</BLOCKQUOTE>
<P>
The second rule is for array initializations:
<BLOCKQUOTE>
<TT>int x[] = { 1, 2, 3, 5, 9 };</TT>
</BLOCKQUOTE>
<P>
The preceding statement creates an array of integers with a length
of 5.
<BLOCKQUOTE>
<TT>StaticInitializer =<BR>
&nbsp;&nbsp;'static' '{' Statement* '}'<BR>
;</TT>
</BLOCKQUOTE>
<P>
You used a static initializer in <A HREF="ch10.htm" >Chapter 10</A>,
&quot;Native Methods and Java,&quot; to load a native library:
<BLOCKQUOTE>
<TT>ParameterList =<BR>
&nbsp;&nbsp;Parameter (',' Parameter)*<BR>
;<BR>
Parameter =<BR>
&nbsp;&nbsp;Type Identifier ('[' ']')*<BR>
;<BR>
Statement =<BR>
&nbsp;&nbsp;VariableDeclaration<BR>
| Expression ';'<BR>
| '{' Statement* '}'<BR>
| 'if' '(' Expression ')' Statement ('else' Statement)?<BR>
| 'while' '(' Expression ')' Statement<BR>
| 'do' Statement 'while' '(' Expression ')' ';'<BR>
| 'for' '(' (VariableDeclaration | Expression ';' | ';')<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Expression?
';' Expression?')' Statement<BR>
| 'try' Statement ('catch' '(' Parameter ')' Statement)*<BR>
&nbsp;&nbsp;&nbsp;('finally' Statement)?<BR>
| 'switch' '(' Expression ')' '{' Statement* '}'<BR>
| 'synchronized' '(' Expression ')' Statement<BR>
| 'return' Expression? ';'<BR>
| 'throw' Expression ';'<BR>
| 'case' Expression ':'<BR>
| 'default' ':'<BR>
| Identifier ':' Statement<BR>
| 'break' Identifier? ';'<BR>
| 'continue' Identifer? ';'<BR>
| ';'<BR>
;</TT>
</BLOCKQUOTE>
<P>
Unlike C, break and continue have an optional identifier. This
enables branching to a label. <TT>For</TT>
loops may declare a new variable just as in C++. Notice that each
loop expression is optional.
<P>
Several control statements (<TT>if</TT>,
<TT>while</TT>, and <TT>for</TT>)
specify an expression in parentheses. Semantically, the expression
must evaluate to a boolean type or an error is issued.
<BLOCKQUOTE>
<TT>Expression =<BR>
&nbsp;&nbsp;Expression '+' Expression<BR>
| Expression '-' Expression<BR>
| Expression '*' Expression<BR>
| Expression '/' Expression<BR>
| Expression '%' Expression<BR>
| Expression '^' Expression<BR>
| Expression '&amp;' Expression<BR>
| Expression '|' Expression<BR>
| Expression '&amp;&amp;' Expression<BR>
| Expression '||' Expression<BR>
| Expression '&lt;&lt;' Expression<BR>
| Expression '&gt;&gt;' Expression<BR>
| Expression '&gt;&gt;&gt;' Expression<BR>
| Expression '=' Expression<BR>
| Expression '+=' Expression<BR>
| Expression '-=' Expression<BR>
| Expression '*=' Expression<BR>
| Expression '/=' Expression<BR>
| Expression '%=' Expression<BR>
| Expression '^=' Expression<BR>
| Expression '&amp;=' Expression<BR>
| Expression '|=' Expression<BR>
| Expression '&lt;&lt;=' Expression<BR>
| Expression '&gt;&gt;=' Expression<BR>
| Expression '&gt;&gt;&gt;=' Expression<BR>
| Expression '&lt;' Expression<BR>
| Expression '&gt;' Expression<BR>
| Expression '&lt;=' Expression<BR>
| Expression '&gt;=' Expression<BR>
| Expression '==' Expression<BR>
| Expression '!=' Expression<BR>
| Expression '.' Expression<BR>
| Expression ',' Expression<BR>
| Expression 'indtanceof' ( ClassName | InterfaceName )<BR>
| Expression '?' Expression ':' Expression<BR>
| ''++'' Expression<BR>
| ''-''Expression<BR>
| '++' Expression<BR>
| '-'Expression<BR>
| Expression '++'<BR>
| Expression '-'<BR>
| '-' Expression<BR>
| '!' Expression<BR>
| '~' Expression<BR>
| '('Expression ')'<BR>
| '(' Type ')' Expression<BR>
| Expression '(' ArgList? ')'<BR>
| 'new' ClassName '(' ArgList? ')'<BR>
| 'new' TypeSpecifier ( '[' Expression ']' )+ ('[' ']')*<BR>
| 'new' '(' Expression ')'<BR>
| 'true'<BR>
| 'false'<BR>
| 'null'<BR>
| 'super'<BR>
| 'this'<BR>
| Identifier<BR>
| Number<BR>
| String<BR>
| Character<BR>
;</TT>
</BLOCKQUOTE>
<P>
Comparison expressions always evaluate to a boolean expression.
<P>
Declaring new arrays can be confusing. The syntax states that
there must be a <TT>new</TT> keyword
followed by a type and one or more defined dimensions: <TT>new
int[2][3]</TT>. A trailing undefined dimension is also
allowed: <TT>new int[2][3][]</TT>.
The following is not legal because there must be one or more defined
dimensions: <TT>new int[]</TT>.
<BLOCKQUOTE>
<TT>ArgList =<BR>
&nbsp;&nbsp;Expression (',' Expression )*<BR>
;<BR>
Type =<BR>
&nbsp;&nbsp;TypeSpecifier ('[' ']')*<BR>
;</TT>
</BLOCKQUOTE>
<P>
Here is the second method for declaring an array: <TT>int[]
name</TT>.
<BLOCKQUOTE>
<TT>TypeSpecifier =<BR>
&nbsp;&nbsp;'boolean'<BR>
| 'byte'<BR>
| 'char'<BR>
| 'short'<BR>
| 'int'<BR>
| 'float'<BR>
| 'long'<BR>
| 'double'<BR>
| ClassName<BR>
| InterfaceName<BR>
;<BR>
Modifier =<BR>
&nbsp;&nbsp;'public'<BR>
| 'private'<BR>
| 'protected'<BR>
| 'static'<BR>
| 'final'<BR>
| 'native'<BR>
| 'synchronized'<BR>
| 'abstract'<BR>
| 'threadsafe'<BR>
| 'transient'<BR>
;<BR>
PackageName =<BR>
&nbsp;&nbsp;Identifier<BR>
| PackageName '.' Identifier<BR>
;<BR>
ClassName =<BR>
&nbsp;&nbsp;Identifier<BR>
| PackageName '.' Identifier<BR>
;<BR>
InterfcaeName =<BR>
&nbsp;&nbsp;Identifer<BR>
| PackageName '.' Identifier<BR>
;</TT>
</BLOCKQUOTE>
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