UIL CS: Java Fundamentals

This is part of the UIL CS study series. See also:

• Number Systems
• Bitwise & Boolean
• Recursion & Loops
• OOP & Generics
• Collections & Algorithms
• Practice Resources

Main topic list: https://www.uiltexas.org/files/academics/UILCS-JavaTopicList2526.pdf

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2. printf (Java)

Common formatting codes

Use: System.out.printf("format", values...);

Width + alignment

• %10d width $10$ right-aligned
• %-10d width $10$ left-aligned
• %05d pad with zeros

Examples

int x = 42;
double pi = Math.PI;
String name = "UIL";

System.out.printf("x=%d%n", x);            // x=42
System.out.printf("pi=%6.3f%n", pi);       // pi= 3.142
System.out.printf("%10d%n", x);            // [       42]
System.out.printf("%-10s%n", name);        // [UIL      ]
System.out.printf("%05d%n", x);            // 00042
System.out.printf("100%% done%n");         // 100% done

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3. Operator Precedence

1. Parentheses: ()
2. Unary: !, ++, --, unary + -
3. Multiply: * / %
4. Add: + -
5. Shift: << >> >>>
6. Relational: < <= > >= instanceof
7. Equality: == !=
8. Bitwise: & then ^ then |
9. Logical: && then ||
10. Ternary: ? :
11. Assignment: = += -= ...

Memorization trick: "PUMA SREBLTA"

• Parentheses
• Unary
• Note: postfix operators return the old value of a variable and update the variable immediately
• Multiplicative
• Additive
• Shift
• Relational
• Equality

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6. Memory Allocated for Java Data Types

Primitive types (fixed sizes)

Reference types

String, arrays, objects, collections store:

• a reference in the variable
• actual object is on the heap

Reference size depends on JVM (commonly $4$ bytes with compressed oops, or $8$ bytes). UIL questions typically focus on primitive sizes.