# lecture4 - Administrative Issues Expressions, Objects, and...

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1 Expressions, Objects, and Class Methods Lecture 4 Administrative Issues • Due Today – Homework 0 • New Assignments – Program 1 Assigned • First real programming assignment WILL BE TIME CONSUMING! WORK OVER THE LONG WEEKEND! From Last Time… • Types, Variables, Assignment • Example: float testAvg; testAvg = 98.43; Identifier Expression Assignment = ; Expressions are much more than just literals! Why Expressions? • How do we find the test average? • Example: int test1, test2, test3; float testAvg; test1 = 95; test2 = 84; test3 = 90; testAvg = WHAT GOES HERE? Expressions Expression – Combination of one or more operands and operators • Operands – Data to be operated on – Constants, Variables, Literals, Objects, … • Operators – The operation to be performed – Addition, Subtraction, Division, … Common Arithmetic Operators 10 % 4 = 2 12 / 4 = 3 3 * 4 = 12 10 – 5 = 5 17 + 2 = 19 Numeric Example (Not Java…) Java Symbol Operation % Remainder / Division * Multiplication - Subtraction + Addition

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2 Operands and Data Types • Type of operands determines type of expression result Integer Both Integers Real Mix of Reals/Integers Real Both Reals Result of Expression Type Operand Types Example Expressions 1.33 4.0 / 3.0 1 4 / 3 1.33 4 / 3.0 12.0 4.0 * 3.0 1.0 4.0 – 3 7 4 + 3 Result Expression Longer Expressions • Combine multiple operations to form long expressions int test1, test2, test3, sum; float testAvg; test1 = 95; test2 = 84; test3 = 90; sum = test1 + test2 + test3; testAvg = sum / 3.0; Order of Operations int num1; num1 = 10 + 10 / 2; What is the value of num1 ? If addition is first, 10 If division first, 15 Order of Operations • Each operator has a precedence level • Operations performed in order of level – Like algebra, * before + • On same level, operations performed left-to-right • Parenthesis used to change order – Example: (5+5)*2 5+5*2 Java’s Precedence Levels 4 3 2 1 Precedence Level = + - + * / % + - Operator Assignment Addition Subtraction String Concatenation Multiplication Division Remainder Unary Plus (Positive) Unary Minus (Neg) Operation
3 Test Average int test1, test2, test3; float testAvg; test1 = 95; test2 = 84; test3 = 90; testAvg = (test1+test2+test3)/3.0; 2 Minute Exercise • What value is returned from each expression? 5+7/2 (5+7)/2 (5+7)/2.0 5.0+7/2 5.0+7.0/2.0 (5+4+3+2+1)/2 6%5+4%3+2%1 Back to Data Types • Recall, not all integers are the same byte , short , int , long • Not all real numbers are the same float , double • Difference is number of bytes used to store data • More bytes more possible values Data Type Conversion • Values can be converted from one type to another • Three ways – Assignment Conversion – Arithmetic Promotion

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## lecture4 - Administrative Issues Expressions, Objects, and...

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