java syntax.pdf

8/14/2019 Java Syntax.pdf

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Basic Java/C SyntaxHarry Erwin, PhDCSE301


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Resources Flanagan, D., 2005,Java in a Nutshell, 5th

edition, OReilly, ISBN 0-596-00773-6

McLaughlin, B, and Flanagan, D, 2004,Java 1.5Tiger: A Developers Notebook, OReilly, ISBN0-596-00738-8

Arnold, K., and Gosling, J., 1998, The JavaProgramming Language, Second Edition,Addison-Wesley


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Topics

Punctuation Operators Statements


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Purpose This is a review of basic C syntax as it is

used by Java

We will review: Punctuation Operators

Statements


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Separators

() are used in method calls {} are used to bracket blocks [] are used for array element access are used in generics (Java 5)


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Block Structure {} Java, like C and C++, is a block structured language.

Programmes are organised as nested blocks (Russian dolls), eachproviding a local referencing environment. Names are visible fromdeclaration to the end of the containing block. Names in innerblocks hide the same names in containing blocks. {} are used todelimit blocks.

Memory is divided into a stack and a random access area (like theheap or free store in C or C++). Primitive types, references toreference types, addresses, and method parameters live in the

stack, which represents the local referencing environment.Reference types live in the random access area.

When you enter a block or declare a variable, the stack grows.When you leave a block, the stack shrinks.


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More Separators

: is used in the ?: operator.

; is a statement terminator. , is used as a separator in various places. . is used for object member access.

@ is used in documentation comments.


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Operators +, -, *, / are used in arithmetic. +, - are also used to give the signs of

numbers. ++, -- are used to increment and decrement. ~ is bitwise complement.

! is boolean NOT.

new is an object creation operator.


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More Operators (type) is used for a type conversion. % gives the integer remainder. + and += are used in String concatenation. > is right shift with sign extension.

>>> is right shift with zero extension.


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Yet More Operators < and and >= are greater than/greater than or

equal.

instanceof is used in type comparison. == is equals (identical value or same

object).

!= is not equal, !(a==b)


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Even Yet More

Operators & is bitwise/boolean AND | is bitwise/boolean OR

^ is bitwise/boolean XOR && is conditional AND (fails as soon as an

element is false)

|| is conditional OR (succeeds as soon as anelement is true)

?: conditional (ternary) operator


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Had Enough Operators?

= is assignment

*=, /=, %=, +=, -=, =, >>>=, &=, ^=, |=are all assignment with the correspondingoperation being performed

i+=1; is the same as i++; or i = i+1; forexample. x &= y; is the same as x = x&y;


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Operator Precedence

and Associativity Operators have precedence and associativity Precedence describes the order in which

they are grouped if there are no ()

Associativity describes how a^b^c isevaluated: (a^b)^c or a^(b^c).

Use parentheses for clarity--having to memorise

this stuff is cruel and unusual punishment.


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Reserved Words abstract, assert, boolean, break, byte, case,

catch, char, class, const, continue, default, do,double, else, enum, extends, false, final,

finally, float, for, goto, if, implements, import,instanceof, int, interface, long, native, new,null, package, private, protected, public,return, short, static, strictfp, super, switch,synchronized, this, throw, throws, transient,true, try, void, volatile, while.

Whew!


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Expression Statements

Expression statements can have side effects.They include:

assignments increments and decrements method calls

object creation

Terminated with a ;


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Empty Statement

A single ; Sometimes useful, particularly in loops.


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Local Variable

Declarations Format is type variableName; May also include an initializer:

type variableName = otherVariable; type variableName = new type(args); String stringName = the string;

Can appear anywhere. Look up scope orlexical scope. Limited to the local block.


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Control Flow

if-else

switch while and do-while for


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if-else

Syntax: if (boolean-expression)

statement1; // true case else // optional, but tricky statement2; // false case

Be careful about which if the else is boundto. It will be bound to the innermost if thatdoesnt yet have an else statement.


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if-if-else

The following is also legal:

if (boolean1) statement1;

else if (boolean2) statement2; etc... // you know what I mean here. else statementN; /* executed if none of

the other statements are executed. */


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switch

switch (integer expression or enumeration type) {

case value1: statement1;

case value2: statement2; break; default: statementDefault; break;

case value3: statement3; break;

}

Note that if case value1 is executed, statements 1 and2 are executed. To prevent that, you use break; orreturn;


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while and do-while

while(boolean expression) statement;

do statement while(boolean expression); The difference is whether the boolean

expression is evaluated before or after thestatement is executed in the loop.


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for

for(init; (boolean expression); incr) statement;

init; is executed once at the beginning,

(boolean expression); is executed at the beginning of eachloop to see if the loop continues.

statement; is executed for each loop. continue; skips to incr;

incr; is executed for each loop

Infinite loop

for (;;) statement;


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Labeled Statement

label: statement;

Used by the break and continue statementsas a destination. break label;

continue label;


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break and continue

A break; statement exits from any block orstatement

A break label; exits from the block orstatement named label. A continue; or continue label; skips to the

end of a loops body.

There is no goto.


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return

return; or return retval; exits the methodand returns to the calling method. The stackgets unwound for this.


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Conclusions

Basic Java syntax is similar to that in C andC++, with some exceptions.

Review it, because we will expect you toknow it from the beginning. There are some differences that we will

cover from time to time.

We will also cover some new stuff in Java 5

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