Top 200 Vocabulary Word List for AP Computer Science A | Must Know Words for Common Examination Instructions

The 200-word examination instruction list

AP Computer Science A instructions tell you whether to trace existing Java, write a method, design a class or change a collection. Before coding, underline the required return type, the input guarantees and any rule about changing the supplied data.

Start with the list below, or jump to exam requirements, worked examples, the Fencing Method or practice. The list combines command words with terms that tell you how to read a question or format an answer.

Java instructions, program behaviour and code vocabulary

No.	Instruction or term	Meaning or action
1	Implement	Write Java code that meets the given method or class specification.
2	Trace	Follow the code in execution order and record how values change.
3	Determine the output	Give exactly what the program prints, including order and spacing when relevant.
4	Return a value	Use return to hand the requested result back to the caller.
5	Modify in place	Change the existing object or collection while preserving its identity.
6	Do not modify the input	Keep the supplied data intact while producing the requested result.
7	Use the provided method	Call the specified helper with the required arguments and use its result appropriately.
8	Method signature	In these examples, identify the Java method name and ordered parameter types.
9	Method header	Read the declaration before the body, including modifiers, return type and parameters where present.
10	Method body	Read or write the statements executed on a call.
11	Parameter	Name a variable declared to receive an argument when a method is invoked.
12	Argument	Identify the expression supplied at the call site.
13	Return type	Identify the type the method promises to return.
14	Void	Indicates that a method returns no value.
15	Call site	Locate the expression or statement where a method is invoked.
16	Instance method	A method invoked on an object that can access its instance state.
17	Static method	A class-level method that can be called without a receiver instance.
18	Class	A definition that specifies members for a type of object.
19	Object	A runtime instance of a class, or an array in Java.
20	Class header	Give the declaration that names the class and any required modifiers.
21	Constructor	Write the initialisation code run when a new instance is created.
22	Constructor header	Use the class name and required parameter list without declaring a return type.
23	Instance variable	Store data separately in each object.
24	Class variable	A static field shared across instances of the class.
25	Local variable	A variable declared within a method, constructor or block.
26	Scope	The region where a name can be used.
27	Field	A variable declared as a member of a class.
28	Initialise	Give a variable or object its starting state.
29	Instantiate	Create a new instance, typically with new.
30	Reference	A value used to refer to an object or array.
31	Alias	A second reference to the same object.
32	Null	A reference value that refers to no object.
33	Primitive type	A built-in value type such as int, double or boolean.
34	Reference type	A type whose values can refer to an object or array or be null.
35	Assign	Evaluate the right side and store the result in the target variable or location.
36	Declaration	Introduce a name with a type or other required declaration information.
37	Expression	A piece of code that evaluates to a value.
38	Statement	A complete instruction or control structure in Java source.
39	Cast	Explicitly request conversion to the target type where Java permits it.
40	Integer division	Divide integer operands and truncate the result toward zero.
41	Remainder operator	Use % to get the remainder after division.
42	Increment	Increase a value by one.
43	Decrement	Decrease a value by one.
44	Compound assignment	Apply an operation and store its result in the same target, such as with +=.
45	Operator precedence	Determine which operator binds first when grouping is implicit.
46	Boolean expression	Evaluate the condition to true or false.
47	Comparison operator	Test a relation such as less than or equality.
48	Logical AND	Evaluate true only when both conditions are true.
49	Logical OR	Evaluate true when either or both conditions are true.
50	Logical NOT	Reverse a Boolean value.
51	Short-circuit evaluation	Skip evaluating a right operand when the left operand already determines the Boolean result.
52	Branch	Select a code path based on a condition.
53	Nested conditional	A conditional statement inside another conditional’s branch.
54	Loop guard	The condition tested to decide whether a loop continues.
55	Loop update	The change made to control state between iterations.
56	Iteration	One repetition of a loop body.
57	Nested loop	A loop inside the body of another loop.
58	Traversal	Visit the required elements in the order the task specifies.
59	Enhanced for loop	Use Java’s for-each syntax to read elements one at a time when an index is unnecessary.
60	Accumulator	A variable updated to build a running result.
61	Counter	A variable that tracks how often an event occurs.
62	Sentinel value	A designated value used to signal a boundary or stopping condition.
63	Off-by-one error	An index or count mistake caused by moving a boundary one position.
64	Index	A zero-based position in a Java array, String or ArrayList.
65	Bounds check	Confirm an index is at least zero and smaller than the structure’s length or size.
66	Array	A fixed-length indexed collection of elements with a common declared type.
67	Array length	Read the number of array slots using length without parentheses.
68	Array initializer	Give an array its starting element values in the specified order.
69	ArrayList	A resizable indexed list that stores reference-type elements.
70	Generic type argument	The type supplied to a generic class, as String in ArrayList<String>.
71	Wrapper class	An object type corresponding to a primitive, such as Integer for int.
72	Size	Use size() to obtain the current number of elements in an ArrayList.
73	Get	Use get(index) to read the existing element at an ArrayList position.
74	Set	Use set(index, value) to replace an existing element without changing list size.
75	Add	Append an element or insert it at a valid position, depending on the overload.
76	Remove	Delete an element using the overload requested and account for later indices shifting.
77	Two-dimensional array	An array whose elements are arrays.
78	Row index	The first index in the usual grid interpretation of a Java 2D array.
79	Column index	The second index within a specified row.
80	Row-major traversal	Visit all relevant columns of each row before advancing to the next row.
81	Column-major traversal	Visit the relevant rows of each column before advancing to the next column.
82	Rectangular array	A 2D array whose rows have the same length.
83	String	An immutable Java sequence of characters used for text.
84	Substring	Use start inclusive and end exclusive indices when both are given.
85	String concatenation	Join text using + and check the grouping when numbers are present.
86	String equality	Use equals when the task compares String contents.
87	Reference equality	Use == to test whether two references refer to the same object or are both null.
88	Lexicographic order	Compare text using the ordering defined by the applicable comparison method.
89	Index of	Use indexOf to find the first matching occurrence, or recognise −1 for no match.
90	Encapsulation	Group state and behaviour and control direct access to internal details.
91	Public member	A member accessible to other code subject to visibility of its enclosing type.
92	Private member	A member intended for use within its defining class.
93	Accessor	A method that reports an aspect of object state.
94	Mutator	A method that changes object state.
95	This reference	Use this to refer to the current object in instance code.
96	Object state	The current values of an object’s fields.
97	Side effect	An observable change, such as updating a field or printing, beyond returning a value.
98	Precondition	A requirement callers may be expected to satisfy before the operation.
99	Postcondition	A result or state change the operation must guarantee afterward.
100	Edge case	An input at or near a boundary that may behave differently.
101	Test case	A specific input and expected result used to check the specification.
102	Dry run	Walk through the code by hand with concrete inputs.
103	Compilation error	A violation detected before normal execution, such as incompatible types.
104	Runtime exception	An exceptional condition occurring during execution.
105	Logic error	Code runs but yields an incorrect result for the intended task.
106	Linear search	Check elements in order until the desired result is found or the search ends.
107	Binary search	Narrow the range repeatedly in data sorted by the relevant ordering.
108	Selection sort	Repeatedly choose an extremal item from the unsorted region and put it in position.
109	Insertion sort	Build a sorted region by inserting each next item into its proper position.
110	Recursion	Solve a problem through method calls on smaller or simpler cases.
111	Base case	A case solved without another recursive call.
112	Recursive case	A case whose result depends on a recursive call and progress toward termination.

Java task constraints and edge cases

No.	Instruction or term	Meaning or action
113	Write a class	Provide the declaration, fields, constructor and methods specified.
114	Complete a method	Fill the method body while preserving its supplied header.
115	Method call	Invoke a method with an appropriate receiver and arguments.
116	Instance creation expression	Use new and the matching constructor arguments to create an object.
117	Overloaded method	A method sharing a name with another but having a different parameter list.
118	Zero-based indexing	Count the first position as zero.
119	Exclusive upper bound	Stop before the named upper index or limit.
120	Inclusive lower bound	Include the lower index or limit if it meets the other conditions.
121	Visit once	Process every required element exactly one time.
122	Preserve order	Keep the relative sequence of items that remain or are returned.
123	Empty list	A list with size zero.
124	Empty string	A String whose length is zero.
125	First match	The earliest eligible element in the required traversal order.
126	Last match	The final eligible element in the required traversal order.
127	Duplicate	An additional occurrence of a value already present under the stated equality rule.
128	Consecutive	Adjacent in the order being examined.
129	Neighbour	A nearby element whose position satisfies the rule in the prompt.
130	Row total	Add the eligible values across one row.
131	Column total	Add the eligible values down one column.
132	Diagonal entry	Use positions satisfying the relevant diagonal’s index rule.
133	Minimum	The smallest eligible value under the specified comparison.
134	Maximum	The largest eligible value under the specified comparison.
135	Tie	A case where competing values have the same ranking.
136	Stable order	Keep the prior relative order of equal-ranking elements when the task requires it.
137	Integer overflow	A fixed-width integer operation produces a value outside its representable range and can wrap.
138	Boolean flag	A variable that stores whether a condition has been met.
139	Loop invariant	A property that stays true at a designated point in each iteration.
140	Exit condition	The condition under which repetition stops.
141	Return early	Finish the method as soon as the required result is known and doing so preserves the contract.
142	Combine conditions	Use the appropriate Boolean operations and grouping to express the full requirement.
143	Sample output	The exact result shown for an example input.
144	Test the smallest allowed case	Use the minimum input size permitted by the specification.
145	System.out.print	Print a value without adding a line separator.
146	System.out.println	Print a value and then add a line separator.
147	Autoboxing	Java automatically converts a primitive value to its corresponding wrapper object where allowed.
148	Unboxing	Java extracts a primitive value from its corresponding wrapper where allowed.
149	Random value	A value generated within the range specified by the operation.
150	Java Quick Reference	Use the supplied reference to confirm listed library methods, parameter order and return types.
151	Boolean value	A value that is either true or false.
152	Index shift	Recalculate which position an element occupies after an insertion or removal.
153	Temporary variable	Store an intermediate value for use in a later expression or operation.
154	Swap	Exchange two values without losing either original value.
155	Pass by value	A method receives a copy of an argument value, including a copied reference for an object argument.
156	Input guarantee	A property the prompt promises, such as all array entries being non-null.

Command words, logic and exam directions

No.	Instruction or term	Meaning or action
157	Identify	Name the requested item or feature directly.
158	State	Give the requested fact or result in a concise form.
159	Describe	Report the relevant features, sequence or pattern.
160	Explain	Connect the result to a cause, mechanism or principle.
161	Compare	Use the same basis for both cases and state the relevant relationship.
162	Contrast	State a difference between the named cases on a common basis.
163	Determine	Use the information given to reach the requested result.
164	Predict	State the outcome expected under the supplied conditions.
165	Justify	Connect specific evidence or a rule to the answer you give.
166	Calculate	Use the supplied values and the relevant relationship to produce a result.
167	Estimate	Give a reasonable approximate value from the information provided.
168	Interpret	Explain what the result means in the scenario.
169	Analyze	Break the information into relevant parts and explain how they relate.
170	Evaluate	Judge the claim, design or result against a stated or relevant criterion.
171	Support	Give evidence that strengthens the named claim.
172	Select	Choose the option that meets the stated condition.
173	Define	State the meaning of the term with its essential features.
174	Give one	Supply one relevant answer that meets the task.
175	Indicate	Point to or state the feature the prompt asks for.
176	Complete	Fill the missing parts while preserving the given structure.
177	Construct	Produce the specified representation using the information given.
178	Outline	Give the main steps or features in a logical order.
179	Infer	Draw a conclusion supported by the clues or evidence supplied.
180	Suggest	Offer a plausible answer that fits the scenario and constraints.
181	Distinguish	Name the feature that separates two easily confused ideas.
182	Demonstrate	Show that a stated claim follows by giving appropriate steps or an example.
183	Check	Test the proposed result against the original conditions.
184	Represent	Express the same information in the requested form.
185	Evidence	A relevant observation, value, result or example that supports a claim.
186	Claim	A statement that can be tested or supported.
187	Assumption	A condition treated as true for the purpose of the reasoning.
188	Constraint	A restriction the answer must satisfy.
189	Criterion	The rule or standard used to judge whether a choice works.
190	Condition	A requirement or circumstance that affects the conclusion.
191	Conclusion	The result of the reasoning stated in the question’s context.
192	Exception	A case that departs from the stated rule.
193	Counterexample	A case that disproves a general claim.
194	Magnitude	The size of a quantity, considered separately from direction.
195	Direction of change	State whether the quantity increases, decreases or stays unchanged.
196	Initial value	The value at the stated starting point.
197	Final value	The value at the stated end point.
198	Signed change	Subtract the initial value from the final value and retain the sign.
199	Relative change	Divide the difference by the initial value when that baseline is meaningful.
200	Sequence	Give the steps or outputs in their required order.

What the AP Computer Science A exam requires

College Board lists the regular 2027 exam for 12 May 2027. Fully digital. Complete both sections in Bluebook. The Java Quick Reference is available in the app.

Section	Format and weight
I · Multiple choice	42 questions in 90 minutes, worth 55%. Most are standalone, with occasional short sets.
II · Free response	4 questions in 90 minutes, worth 45%. Prepare for methods and control structures, class design, ArrayList data tasks and 2D array tasks.
Calculator policy	College Board prohibits calculators for this course except for students with an approved four-function calculator accommodation.

AP is a U.S.-based subject examination programme taken by students in the United States and internationally. Practise with the College Board materials for the exact course. If you are taking the exam outside the U.S., confirm registration and local reporting time with your school or test centre. The same vocabulary strategy transfers to other national exams by matching the verb, scope and answer format to that exam’s own sample paper and scoring guidance.

Write down the requested signature and work through a small example before typing the body. Track return values and changes to objects separately. Check the first and last legal indices and any input size allowed by the prompt.

Read the method contract before typing

Copy the required method name and parameter list into your working plan. Identify what the method returns and whether the supplied object changes. If the method is meant to update an instance field, make that update before returning any new value the contract requires.

Use a tiny trace to check loop boundaries

Choose an example with two or three elements and label the indices. After each loop step, write the index and relevant variable values. If elements are removed during traversal, redraw the list after each deletion. This shows which original values are still waiting to be checked.

Test the cases the prompt allows

If an empty list is allowed, use it as a test. If every row is guaranteed to have at least one entry, focus on boundaries within that guarantee. The Java Quick Reference can confirm available methods, but the prompt tells you which inputs to support and whether the operation must preserve order or identity.

Worked examples for common exam instructions

Implement a method that returns a count

Prompt. Write a method that returns the number of strings in a non-null ArrayList of non-null strings that start with A. Leave the list unchanged.

Answer. Start an integer counter at zero. For each string s, test s.length() > 0 && s.substring(0, 1).equals(“A”). Increment the counter on a match and return the counter after the loop.

public int countStartingWithA(ArrayList<String> values) {
    int count = 0;
    for (String s : values) {
        if (s.length() > 0 && s.substring(0, 1).equals("A")) {
            count++;
        }
    }
    return count;
}

The length test protects the substring call because && short-circuits. No list elements are added, removed or replaced.

Design a class with a persistent field

Prompt. A Counter object starts at a supplied integer and exposes an add method that increases its stored value by the amount supplied and returns the updated value.

Answer. Declare a private int field named value. The constructor Counter(int start) assigns value = start. The method public int add(int amount) updates value += amount and returns value.

public class Counter {
    private int value;

    public Counter(int start) {
        value = start;
    }

    public int add(int amount) {
        value += amount;
        return value;
    }
}

An instance field persists across calls and each object has its own value. A local variable declared inside add would not maintain the required state.

Modify an ArrayList while preserving order

Prompt. Remove every negative Integer from a non-null ArrayList of non-null values. Preserve the order of the values left in the same list.

Answer. Visit indices from values.size() − 1 down to zero. At each index i, if values.get(i) < 0, call values.remove(i).

public void removeNegatives(ArrayList<Integer> values) {
    for (int i = values.size() - 1; i >= 0; i--) {
        if (values.get(i) < 0) {
            values.remove(i);
        }
    }
}

On removal, positions to the right shift left, but the next position to visit is to the left. Backward traversal also handles consecutive negative entries.

Translate a 2D array specification

Prompt. Return the number of positive entries in a non-null rectangular int grid. An empty grid is allowed.

Answer. Start count at zero. For each row r from zero to grid.length − 1, check columns c from zero to grid[r].length − 1. Increment count when grid[r][c] > 0. Return count after both loops.

public int countPositive(int[][] grid) {
    int count = 0;
    for (int r = 0; r < grid.length; r++) {
        for (int c = 0; c < grid[r].length; c++) {
            if (grid[r][c] > 0) {
                count++;
            }
        }
    }
    return count;
}

Using grid[r].length inside the outer loop means an empty grid never causes a read of grid[0]. The return after both loops lets the method finish counting every row.

Use the Fencing Method to build an answer

Start within a small boundary. Answer one instruction correctly in a short sentence or a small piece of code. Add one detail at a time, checking that each addition helps satisfy the prompt. Finish by transferring the same skill to a nearby case.

Start. Return the number of matches.

Add context. Visit each element once, count matches and return after the loop.

Add the reasoning or operation. Start count at zero, test each string for a nonempty prefix before taking its substring, increment only for a match and return after the traversal.

Transfer. Change the prompt to remove matches from the input list. Use a trace with two adjacent matches to check whether your index strategy meets the new contract.

Practice with the 200 terms

Choose three terms with different answer shapes. Cover the meaning column and say what an examiner would expect to see. Write one answer to each, then underline the exact number, evidence, explanation or code that fulfils the instruction.

Trace versus implement

Try it. Trace the backward-removal method on [−2, −1, 4, −3], then write one test case that checks that a list with no negative numbers is unchanged.

Check. The successive deletions produce [−2, −1, 4], [−2, 4], and then [4]. For the additional test, use [0, 2] and expect the same list with contents [0, 2].

On a second pass, test the examples in the question and one boundary case allowed by the specification. Practise typing an entire free response in a plain editor, then compare it with the published scoring guidelines for a released question.

Frequently asked questions

Does a code-writing task need a prose explanation?

When the prompt asks you to implement, give the Java code it requests. Use a short private trace to verify the result and preserve any given header or class details.

Do I have to memorise every definition?

Use the terms in small groups. For each one, practise identifying the required answer and producing it. The exact instructions and official scoring guidelines for an individual item determine what that response needs.

Official sources and next reading

College Board AP Computer Science A exam format, course description and released questions · College Board AP calculator policy

AP exam command words · eduKateSG vocabulary learning guide · How to build a sentence with the Fencing Method

College Board exam reference materials