Key Points

• Boolean Expressions & Operators
• Understand the basic Boolean literals: true and false.
• Know the specific operators: relational operators (<, >, <=, >=, ==, !=) and logical operators (&&, ||, !).
• Operator Precedence: In Java, the && operator is evaluated before || unless parentheses change the order.
• Short-Circuit Evaluation: In expressions like A || B or A && B, evaluation stops as soon as the overall truth value is determined.
• De Morgan’s Laws: These allow you to rewrite expressions (e.g., !(x < 5 || y > 10) is equivalent to x >= 5 && y <= 10).

• if Statements and Control Flow
• Syntax: Use the if statement (with optional else or else if clauses) to control the flow based on Boolean conditions.
• Nested if Statements: Be aware that an else pairs with the nearest preceding unmatched if.
• Execution Order: Understand how the order of conditions affects which block of code executes.

• Iterative Statements & Testing
• Iteration: Use loops (for, while, do-while) to repeat code segments.
• do-while Loop: Executes the loop body at least once.
• Testing: Validate your code using test cases to catch errors and ensure the implementation meets the method’s specifications.
• Equivalence: Learn to determine when two different code segments yield equivalent results (both logically and in output).

• Comparing Objects & Object Creation
• Reference vs. Content Comparison: The == operator checks for reference (memory) equality, whereas the equals() method is used to check for content equality.
• Object Creation: Use the new keyword to instantiate objects and then call methods on these objects.
• Method Specifications: Write code that satisfies given method requirements using expressions, conditionals, and loops.

Sample Code Snippets

1. Boolean Expressions and Operator Precedence

2. if Statements and Control Flow (Nested if-else)

3. Using Iterative Statements (for and while loops)

4. Comparing Objects

5. Creating Objects and Calling Methods

20 AP-Style Multiple Choice Questions

1. Boolean Expression Evaluation:
What is the value of the following expression?
A) true
B) false
C) Compilation error
D) Depends on runtime conditions

2. if Statement Binding:
Given the code below, what is printed when the code is executed?
A) A
B) B
C) A followed by B
D) Nothing is printed

3. Complex Boolean Evaluation:
What is the value of the following expression?
A) true
B) false
C) Compilation error
D) Depends on operator precedence

4. for Loop with Break:
What is the output of the following code segment?
A) 01234
B) 012
C) 0123
D) 123

5. Equivalent Code Segments:
Which pair of code segments below produce equivalent outputs?
• Segment A:
• Segment B:
A) They are equivalent for all values of x.
B) They are not equivalent when x is 0.
C) They are equivalent only for positive x.
D) They are equivalent only for negative x.

6. Short-Circuit Evaluation:
Consider the following code. What is printed?
A) X
B) Y
C) Compilation error
D) Nothing is printed

7. Operator Precedence:
Which operator has higher precedence in Java?
A) &&
B) ||
C) Both have the same precedence
D) Depends on the operands

8. if-else Example:
What is printed by the following code?
A) Even
B) Odd
C) None
D) No output due to a logic error

9. Assignment in Condition:
What is wrong with the following code?
A) Nothing is wrong
B) The condition is always true
C) Compilation error: cannot convert int to boolean
D) Runtime error

10. Object Comparison:
Which of the following is used to compare objects for content equality?
A) ==
B) equals()
C) compareTo()
D) isEqual()

11. Code Equivalence:
Determine if the following two code segments yield equivalent results:
• Segment 1:
• Segment 2:
A) Yes, they are equivalent.
B) No, they differ when x equals 10.
C) No, they differ when x is negative.
D) They are equivalent only for positive values of x.

12. Short-Circuit Concept:
Which statement best describes “short-circuit” evaluation?
A) Every part of a boolean expression is evaluated regardless of its outcome.
B) Evaluation stops as soon as the overall truth value is determined.
C) The order of evaluation is from right-to-left.
D) Boolean expressions are only evaluated when used in loops.

13. while Loop Execution:
What will be the output of the following code?
A) 123
B) 012
C) 321
D) 210

14. Object Creation Syntax:
Which of the following is the correct statement for creating an object in Java?
A) MyClass obj = MyClass();
B) MyClass obj = new MyClass;
C) MyClass obj = new MyClass();
D) MyClass obj = new MyClass{};

15. Method Implementation for Specification:
Given the specification “Write a method that returns true if the input integer is even, false otherwise,” which of the following implementations is correct?
A)
B)
C) Both A and B
D) Neither A nor B

16. Object Equality vs. Reference Equality:
When comparing objects in Java, the == operator checks for:
A) Content equality
B) Reference (memory address) equality
C) Both content and reference equality
D) None of the above

17. Loop Types:
Which iterative statement is guaranteed to execute its loop body at least once?
A) for loop
B) while loop
C) do-while loop
D) All of the above

18. Nested if Statement Analysis:
Examine the following code segment:
What does this code determine?
A) The minimum of a, b, and c
B) The maximum of a, b, and c
C) The median of a, b, and c
D) The sum of a, b, and c

19. Code Blocks Delimitation:
In Java, which of the following symbols is used to denote a block of code?
A) Parentheses ()
B) Curly braces {}
C) Square brackets []
D) Angle brackets <>

20. De Morgan’s Law Application:
Which of the following expressions is equivalent to the boolean expression !(x < 5 || y > 10)?
A) x >= 5 && y <= 10
B) x >= 5 || y <= 10
C) x < 5 && y > 10
D) x < 5 || y > 10

优先级问题：

1. 逻辑非（!）
• 这是一个一元运算符，用于对布尔值取反。

2. 逻辑与（&&）
• 在 ! 运算符之后进行计算，只有当两个操作数都为 true 时，结果才为 true。

3. 逻辑或（||）
• 最后计算，只要有一个操作数为 true，结果就是 true。

the use of “==”：

1. 基本类型的比较
• 当用于基本数据类型（如 int、char、boolean 等）时，== 比较的是它们的实际值。
• 示例：

2. 引用类型的比较
• 当用于对象时，== 检查的是两个引用是否指向同一个内存地址，也就是是否引用的是同一个对象。
• 示例：
• 尽管 s1 和 s2 的内容相同，但它们是两个不同的对象，因此 s1 == s2 返回 false。

the use of do-while：