Java Tokens

In this section we will discuss

1. Literals

2. Identifiers

3. Keywords

4. Operators

5. Comments

Literals

In the previous sections I have already clarified what are Literals they are called constants. These are the values that do not change or cannot accept any other value except their own.

int a=0;

In the above Java statement the numeral zero represents a ‘Literal’. It represents a value which cannot be changed thus it is called a ‘Literal’ or ‘Constant’. These values may represent character, integer, float or Boolean type of values. I had told you about two basic types of literals alpha-numeric and numeric. Let’s see these in a bit more detail in relation to Java.(These are known as primitive data type)

byte: The byte data type is an 8-bit signed integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory.  short: The short data type is a 16-bit signed integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive).  int: The int data type is a 32-bit signed  integer. It has a minimum value of -2,147,483,648 and a maximum value of 2,147,483,647 (inclusive). For integral values, this data type is generally the default choice unless there is a reason to choose something else. This data type will most likely be large enough for the numbers your program will use, but if you need a wider range of values, use long instead. long: The long data type is a 64-bit signed integer. It has a minimum value of -9,223,372,036,854,775,808 and a maximum value of 9,223,372,036,854,775,807 (inclusive). Use this data type when you need a range of values wider than those provided by int. float: The float data type is a single-precision 32-bit IEEE 754 floating point. This data type should never be used for precise values, such as currency. double: The double data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency. boolean: The boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined. char: The char data type is a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of '\uffff' (or 65,535 inclusive). Examples of Boolean literal true, false Example of float literals 2.3f , 4.089f Example of double literal 0.0d , 0.5555d Example of int literals 3456, 5678 Example char literal ‘s’, ‘\n’ Identifiers Identifiers are also known as variables. Basically variables are memory locations where we store any value we require for further computation during the program execution. They are like containers, empty by itself but useful when filled with some value. Example a water bottle is empty to begin with but it stores the amount of water you pour in. It depends if you want to fill the whole water bottle or part of it. Same way memory locations on the computer memory are empty by default but can be used to store data you require. Thus each memory location can be given any name. It totally depends on you as long as you follow some simple naming conventions it is ok with the compiler. The rules to for naming a variable are you can use letters from A to Z as well as lowercase representation a to z any integer number can be used as long as the name does not start with a number no special character can be used except underscore Some of the good programming practices dictate few more rules, please be advised that rules mentioned below are guidelines and are not implemented or checked by the Java compiler the variable name should be something which makes the it easy to understand what value is stored inside the name should be descriptive rather than cryptic bs is not a good name instead you can use basic_salary Variable name Valid/Invalid basic_sal valid 12salalry Invalid basic*sal invalid Keywords These are special words which have been reserved for use in Java and you cannot use them as identifier name. They can be used to perform some task or give a command to the compiler. Some of the Java keywords are abstract continue for new switch assert default goto package synchronized boolean do if private this break double implements protected throw byte else import public throws case enum instanceof return transient catch extends int short try char final interface static void class finally long strictfp volatile const float native super while Operators These are mathematical or logical symbols used to perform some operation on one or more values. Java supports the following type of operators Simple Assignment Operator =          Simple assignment operator Arithmetic Operators +          Additive operator (also used for String concatenation) -           Subtraction operator *           Multiplication operator /           Division operator %         Remainder operator Unary Operators +          Unary plus operator; indicates positive value (numbers are positive without this, however) -           Unary minus operator; negates an expression ++        Increment operator; increments a value by 1 --          Decrement operator; decrements a value by 1 !           Logical compliment operator; inverts the value of a boolean Equality and Relational Operators ==        Equal to !=         Not equal to >          Greater than >=        Greater than or equal to <          Less than <=        Less than or equal to Conditional Operators &&        Conditional-AND ||           Conditional-OR ?:      Ternary (shorthand for if-then-else statement) Type Comparison Operator instanceof         Compares an object to a specified type Bitwise and Bit Shift Operators ~          Unary bitwise complement <<        Signed left shift >>        Signed right shift >>>      Unsigned right shift &          Bitwise AND ^           Bitwise exclusive OR |           Bitwise inclusive OR Operator Precedence In math’s we have BODMAS which defines precedence of the operators. In the same way Java too has its own rules for operator precedence  The operators in Java, shown in order of precedence - from highest to lowest Priority Operators Operation Associativity 1 [ ] array index left () method call . member access 2 ++ pre- or postfix increment right -- pre- or postfix decrement + - unary plus, minus ~ bitwise NOT ! boolean (logical) NOT (type) type cast new object creation 3 * / % multiplication, division, remainder left 4 + - addition, substraction left + string concatenation 5 <<  signed bit shift left left >>  signed bit shift right >>>  unsigned bit shift right 6 < <= less than, less than or equal to left > >= greater than, greater than or equal to instanceof reference test 7 == equal to left != not equal to 8 & bitwise AND left & boolean (logical) AND 9 ^ bitwise XOR left ^ boolean (logical) XOR 10 | bitwise OR left | boolean (logical) OR 11 && boolean (logical) AND left 12 || boolean (logical) OR left 13 ? : conditional right 14 = assignment right *= /= += -= %=      <<= >>= >>>=      &= ^= |= combinated assignment (operation and assignment) Comments Comments are non-executable lines of java code. They are put in the program for documentation and future reference. Java compiler ignores these lines.There are two types of comments a)     single line coment These comments begin with a // b)    Multi line comments These comments start with /* and end with */