Software Engineers Handbook/Language Dictionary/Java

Java edit

Here is the Java wikipedia entry.

Type edit

Java is a full, procedural, object-oriented language.

Execution Entry Point edit

public static void main(String args[])
    // some functionality here

General Syntax edit

The typical statement is completed by a semi-colon. For the assignment of b to a use:

a = b;

Comments edit

// this is an inline comment.  Everything after the // is a comment.

Block comments are specified by a starting /* and ending */ They can span multiple lines.

 * this is a block comment 

Variable Declarations edit

int x = 9;
Integer y = new Integer(4);

Method Declaration/Implementation edit

// declaration
private return_type class_name::function_name(argument_1_type arg_1_name, 
                          argument_2_type arg_2_name, 
                          default_argument_type default_arg_name)
{ // implementation
    // work with arg_1_name, arg_2_name, and default_arg_name
    // depending on the argument types the variables are passed by 
    //   value, reference, or are constant
    // don't forget to return something of the return type
    return 36;

Scope edit

Scope is defined by curly braces.

{ // this the beginning of a scope
    // the scope is about to end

Conditional Statements edit

If and only if A is equal to B assign C to D, otherwise, assign E to F.

if( A == B )
    D = C;
    // more code can be added here.  It is used if and only if A is equal to B
    F = E;
    // more code can be added here.  It is used if and only if A is not equal to B


if( A == B ) 
    D = C; //more lines of code are not permitted after this statement
    F = E;

Alternatively, a switch statement can be used for multiple choice operations. This sample converts a number input to text.

switch( number_value )
    case 37:
        text = "thirty-seven";
        break; // this line prevents the program from writing over this value with the
               //   following code
    case 23:
        text = "twenty-three";
    default: // this is used if none of the previous cases contain the value
        text = "unknown number";

Looping Statements edit

This code counts from 0 to 9, adding up the contents of the array.

int i = 0;
for( int index = 0; index < 10; index = index + 1 )
    i = array[index];

This code repeats until the number 4 is found. If this runs off of the end of the array, there could be a problem.

int index = 0;
while( 4 != array[index] )
    index = index + 1;

This code increments the counter before the check is made, so that it starts with element 1.

int index = 0;
    index = index + 1;
while( 4 != array[index] );

Output Statements edit

System.out.println( "Hello World!" );

Containers edit

Containers inherit from the Collection class. See the java.util package for specific containers including List, LinkedList, Queue, Stack, Dictionary and HashMap.

Algorithms edit

The Collection class has algorithms like sort.

Garbage collection edit

Garbage collection is automatic.

Physical Structure edit

Code is generally kept in files with a .java extension. It is compiled into Java byte code into files with .class extensions.

Tips edit

  • Classes in the Java packages are capitalized, methods are not.
  • Everything is a pointer. Use a clone method to avoid operating on the original element of a Collection.
  • Arrays start with index 0.
  • Don't confuse these two:
=  // assignment
== // comparison, is equal to

Often using the one you don't want will compile, and will produce results you did not expect.

Web References edit

Books and Articles edit

paper references here