Java Handouts

elm Seekho
Basics of java


Collection raw facts & figures or unprocessed and meaningless form which does not create any sense in known as data e.g. 1 + 1 =  ?, where 1 + 1 is data because it does not create any sense until unless we complete the equation.


In contrast the processed and meaningful form is known as information, which further helps us for making decision e.g. 1 + 1 = 2 where “2” is information. Information can also act as data.


A computer is a programmable machine that receives input, stores and manipulates data, and provides output in a useful format.

A computer does not need to be electric, nor even has a processor, nor RAM, nor even hard disk. The minimal definition of a computer is anything that transforms information in a purposeful way. Computer divided into two parts i.e. hardware & software.


A general purpose computer has four main components: the arithmetic logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by busses, often made of groups of wires.

Inside each of these parts are thousands to trillions of small electrical circuits which can be turned off or on by means of an electronic switch. Each circuit represents a bit (binary digit) of information so that when the circuit is on it represents a “1”, and when off it represents a “0”. The combination of 8-bits forms byte, the representation of any symbol. The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) is collectively known as a central processing unit (CPU). CPU is also known as microprocess


The control unit (often called a control system or central controller) manages the computer’s various components; it reads and interprets (decodes) the program instructions, transforming them into a series of control signals which activate other parts of the computer.

The control system’s functions is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:

  1. Read the code for the next instruction from the cell indicated by the program counter.
  2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
  3. Increment the program counter so it points to the next instruction.
  4. Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
  5. Provide the necessary data to an ALU or register.
  6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
  7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.
  8. Jump back to step (1).


The ALU is capable of performing two classes of operations: arithmetic and logic.

The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc.) and square roots.

An ALU may also compare numbers and return Boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other (“is 64 greater than 65?”).

Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing Boolean logic.


Computer main memory comes in two principal varieties: random-access memory or RAM and read-only memory or ROM.

RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer’s initial start-up instructions. In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely.

In a PC, the ROM contains a specialized program called the BIOS that help loading the computer’s operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often called firmware, because it is notionally more like hardware than software.

Flash memory blurs the distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is typically much slower than conventional ROM and RAM however, so its use is restricted to applications where high speed is unnecessary.


In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory (RAM). Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer’s part.


The CPU contains a special set of memory cells called registers that can be read and written too much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed.

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