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Outline

Learn about arithmetic operations, data conversion, operators precedence, assignment operators, and interactive programs in Java. Understand expressions, variables, primitive data types, and more.

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Outline

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  1. Outline Character Strings Variables and Assignment Primitive Data Types Expressions Data Conversion Interactive Programs Graphics Applets Drawing Shapes

  2. Expressions • Expression • Combination of one or more operators and operands • Arithmetic operations • Binary operations • Addition(+), Subtraction(-), multiplication(*), Division(/) • Remainder(%) • Example: 17%4 = 1, 3%8 = 8 • Unary operations (rarely used) • Example: -1; -4; +5

  3. Result of an arithmetic operation • If either or both operands • Used by an arithmetic operator are floating point • Then the result is a floating point • Result is floating point value • If both or • either operands are floating point values • 3.4 + 5 = 8.4

  4. Division • However, division operation is less intuitive • If both operands are integer => integer division • 10/4 = 2 • If either or both are floating point=> floating point division • 10.0/4 and 10/4.0 and 10.0/4.0 are all 2.5

  5. Operator precedence • Expressions are evaluated • according to operator precedence hierarchy • It follows the same rules learned in Algebra • Multiplications, divisions and remainder are performed • Prior to addition, and subtraction • Precedence can be forced by using parentheses • (14+8)/2; • Arithmetic operators with the same precedence • Are evaluated from left to right

  6. Operator precedence (cont’d) Highest priority Lowest priority

  7. Operator Precedence • What is the order of evaluation in the following expressions? a + b + c + d + e a + b * c - d / e 1 2 3 4 3 1 4 2 a / (b + c) - d % e 2 1 4 3 a / (b * (c + (d - e))) 4 3 2 1

  8. Assignment revisited • The assignment operator • Has a lower precedence than arithmetic operators First the expression on the right hand side of the = operator is evaluated answer = sum / 4 + MAX * lowest; 4 1 3 2 Then the result is stored in the variable on the left hand side

  9. Assignment revisited (cont’d) • The right and left sides of an assignment • Can contain the same variable First, one is added to the original value of count count = count + 1; Then the result is stored back into count (overwriting the original value)

  10. Example • Program (TempConverter) • Converts a particular Celsius temperature value • To its equivalent Fahrenheit value using the expression • See TempConverter.java

  11. Increment and decrement a variable • There are three ways • To increment or decrement a variable, it may appear • On both the left-hand side and the right-hand side • count = count +1; or count = count – 1; • The left-hand side • of an increment(++) or decrement(--) operator (postfix form) • count++; or count–-; • The right-hand side • of an increment(++) or decrement(--) operator (prefix form) • ++count; or -–count;

  12. Increment and decrement operators • The increment and decrement operators use only • One operand • The increment operator (++) adds one to its operand • As such, count++; <=> count = count + 1; • The decrement operator (--) subtracts one from operand • As such, count--; <=> count = count - 1; • Increment and decrement operators can be used • In postfix form : count++; • or Prefix form: ++count;

  13. Postfix and prefix forms • When used alone • the prefix and postfix forms are equivalent • It doesn’t matter if you write • count++; or ++count; • In a larger expression • they can yield different results • Total = count++; • Total = ++count;

  14. Assignment operators: main idea • Often we perform • An operation on a variable, and then • Store the result back into that variable • Java provides assignment operators • To simplify that process • For instance • num += count;  num = num + count;

  15. Assignment operators • Many assignment operators are defined in JAVA • += performs addition • Total += 5; is equivalent to Total = Total + 5; • -= performs subtraction • result -= a + b; <=> result = result – (a + b); • /= performs division • highest /= 4; <=> highest = highest/4; • *= performs multiplication

  16. Behavior of assignment operators • The behavior of some assignment operators • Depends on the types of the operands • If the operands to the += • Are strings => operator performs string concatenation • The behavior of an assignment operator (+=) • is always consistent with the behavior of the • corresponding operator (+)

  17. Outline Character Strings Variables and Assignment Primitive Data Types Expressions Data Conversion Interactive Programs Graphics Applets Drawing Shapes

  18. Data conversion • Sometimes, • It is convenient to convert data from • one type to another • For example • in a particular situation we may want to treat • An integer as a floating point value • These conversions • Do not change the type of a variable • nor the value stored in it • They only convert a value as part of a computation

  19. Data conversion • Widening conversions • It is safe • to convert from a byte type to a short type • Since byte is stored in 8 bits • whereas short in 16 bits • There is no loss of information, • and the numeric value is preserved exactly

  20. Data conversion (cont’d) • Narrowing conversions • Go from one type • to a type that uses less space • As such, some of the information • may be compromised • In general, they must be avoided

  21. Conversion techniques • In JAVA, conversion can occur in three ways • Assignment conversion • When a value of one type is assigned • to a variable of another type • Promotion • When operators need to modify their operands • in order to perform the right operation • Casting • The most general form of conversion

  22. Assignment conversion • Assignment conversion occurs • When a value of one type • is assigned to a variable of another type • if money is a float variable and dollars is an int variable • money = dollars=> dollars converted to float • Only widening conversions can be accomplished • Via an assignment • Note that the value or type of dollars did not change

  23. Conversion via promotion • It occurs automatically • When certain operators need • to convert their operands to perform operations • If sum is a float and count is an integer • The value of count is converted to float to perform calculation • result = sum/count;

  24. Conversion using casting • It is • the most general form of conversion in JAVA • a JAVA operator • Specified by a type name in parentheses: (float) for instance • placed in front of the value to be converted • float money = 84.69; int dollars; dollars = (int) money; => dollars = 84

  25. Casting: analysis • Casting is the most powerful and dangerous • Both widening and narrowing conversions • Can be accomplished by casting a value • To cast • The type is put in parentheses in front of the value • Being converted

  26. Conversion using casting (cont’d) • It is helpful • To treat a value temporarily as another type • For example, if total and count are integers • But we want a floating point result when dividing them • int total, count; float result; result = (float) total / count;

  27. Outline Character Strings Variables and Assignment Primitive Data Types Expressions Data Conversion Interactive Programs Graphics Applets Drawing Shapes

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