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Computer Science AB: Quick Reference Guide

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Computer Science AB
class java.lang.Object
// all classes inherit and may override these methods
  • boolean equals(Object other)
  • String toString()
  • int hashCode()
interface java.lang.Comparable
  • int compareTo(Object other)
    // return value < 0 if this is less than other
    // return value = 0 if this is equal to other
    // return value > 0 if this is greater than other
class java.lang.Integer implements java.lang.Comparable
  • Integer(int value)
    // constructor
  • int intValue()
class java.lang.Double implements java.lang.Comparable
  • Double(double value)
    // constructor
  • double(double value)
class java.lang.String implements java.lang.Comparable
  • int length()
  • String substring(int from, int to)
    // returns the substring beginning at from
    // and ending at to-1
  • String substring(int from)
    // returns substring(from, length())
  • int indexOf(String s)
    // returns the index of the first occurrence of s;
    // returns -1 if not found
class java.lang.Math
  • static int abs(int x)
  • static double abs(double x)
  • static double pow(double base, double exponent)
  • static double sqrt(double x)
class java.util.Random
  • int nextInt(int n)
    // returns an integer in the range from 0 to n-1 inclusive
  • double nextDouble()
    // returns a double in the range [0.0, 1.0)
interface java.util.List
  • boolean add(Object x)
    // appends x to the end of list; returns true
  • int size()
  • Object get(int index)
    // returns the element at the specified position
  • Object set(int index, Object x)
    // replaces the element at index with x
    // returns the element formerly at the specified position
  • Iterator iterator()
  • ListIterator listIterator()
class java.util.ArrayList implements java.util.List
  • Methods in addition to the List methods:
  • void add(int index, Object x)
    // inserts x at position index, sliding elements
    // at position index and higher to the right
    // (adds 1 to their indices) and adjusts size
  • Object remove(int index)
    // removes element from position index, sliding elements
    // at position index + 1 and higher to the left
    // (subtracts 1 from their indices) and adjusts size
    // returns the element formerly at the specified position
class java.util.LinkedList implements java.util.List
  • Methods in addition to the List methods:
  • void addFirst(Object x)
  • void addLast(Object x)
  • Object getFirst()
  • Object getLast()
  • Object removeFirst()
  • Object removeLast()
interface java.util.Set
  • boolean add(Object x)
  • boolean contains(Object x)
  • boolean remove(Object x)
  • int size()
  • Iterator iterator()
class java.util.HashSet implements java.util.Set
class java.util.TreeSet implements java.util.Set

interface java.util.Map
  • Object put(Object key, Object value)
    // associates key with value
    // returns the value formerly associated with key
    // or null if key is not in the map
  • Object get(Object key)
  • Object remove(Object key)
  • boolean containsKey(Object key)
  • int size()
  • Set keySet()
class java.util.HashMap implements java.util.Map
class java.util.TreeMap implements java.util.Map

interface java.util.Iterator
  • boolean hasNext()
  • Object next()
  • void remove()
interface java.util.ListIterator extends java.util.Iterator
  • Methods in addition to the Iterator methods
  • void add(Object x)
  • void set(Object x)
Implementation classes for linked list and tree nodes

Unless otherwise noted, assume that a linked list implemented from the ListNode class does not have a dummy header node.
public class ListNode
{  
  private Object value;
  private ListNode next;
  
  public ListNode(Object initValue, ListNode initNext)
    { value = initValue; next = initNext; }

  public Object getValue() { return value; }
  public ListNode getNext() { return next; }

  public void setValue(Object theNewValue) { value = theNewValue; }
  public void setNext(ListNode theNewNext) { next = theNewNext; }
}
Unless otherwise noted, assume that a tree implemented from the TreeNode class does not have a dummy root node.
public class TreeNode
{
  private Object value;
  private TreeNode left;
  private TreeNode right;
  
  public TreeNode(Object initValue)
    { value = initValue; left = null; right = null; }

  public TreeNode(Object initValue, TreeNode initLeft, TreeNode initRight)
    { value = initValue; left = initLeft; right = initRight; }

  public Object getValue() { return value; }
  public TreeNode getLeft() { return left; }
  public TreeNode getRight() { return right; }

  public void setValue(Object theNewValue) { value = theNewValue; }
  public void setLeft(TreeNode theNewLeft) { left = theNewLeft; }
  public void setRight(TreeNode theNewRight) { right = theNewRight; }
}


 
Interface for stacks (* See note at end of reference)

public interface Stack 
{ 
  /**
   * postcondition: returns true if stack is empty; 
   *                otherwise, returns false 
   */
  boolean isEmpty();
 
  /**
   * precondition:  stack is [e1, e2, ..., en] with n >= 0 
   * postcondition: stack is [e1, e2, ..., en, x] 
   */
  void push(Object x); 

  /**
   * precondition:  stack is [e1, e2, ..., en] with n >= 1 
   * postcondition: stack is [e1, e2, ..., e(n-1)]; returns en 
   * exceptions:    throws an unchecked exception if the stack is empty 
   */
  Object pop(); 

  /**
   * precondition:  stack is [e1, e2, ..., en] with n >= 1 
   * postcondition: returns en 
   * exceptions:    throws an unchecked exception if the stack is empty 
   */
  Object peekTop(); 
} 


Interface for queues (* See note at end of reference)

public interface Queue 
{ 
  /**
   * postcondition: returns true if queue is empty;
   *                otherwise, returns false 
   */
  boolean isEmpty(); 

  /**
   * precondition:  queue is [e1, e2, ..., en] with n >= 0 
   * postcondition: queue is [e1, e2, ..., en, x] 
   */
  void enqueue(Object x); 

  /**
   * precondition:  queue is [e1, e2, ..., en] with n >= 1 
   * postcondition: queue is [e2, ..., en]; returns e1 
   * exceptions:    throws an unchecked exception if the queue is empty 
   */
  Object dequeue(); 

  /**
   * precondition:  queue is [e1, e2, ..., en] with n >= 1 
   * postcondition: returns e1 
   * exceptions:    throws an unchecked exception if the queue is empty 
   */
  Object peekFront(); 
} 



Interface for priority queues (* See note at end of reference)

public interface PriorityQueue 
{ 
  /**
   * postcondition: returns true if the number of elements in
   *                the priority queue is 0; 
   *                otherwise, returns false 
   */
  boolean isEmpty(); 

  /**
   * postcondition: x has been added to the priority queue; the number 
   *               of elements in the priority queue is increased by 1. 
   */
  void add(Object x); 

  /**
   * postcondition: The smallest item in the priority queue is removed 
   *                and returned; the number of elements in the priority 
   *                queue is decreased by 1. 
   * exceptions:    throws unchecked exception if priority queue is empty 
   */
  Object removeMin(); 

  /**
   * postcondition: The smallest item in the priority queue is returned; the 
   *                priority queue is unchanged 
   * exceptions:    throws unchecked exception if priority queue is empty 
   */
  Object peekMin(); 
} 

* Note regarding use of stacks, queues, and priority queues

When a stack, queue, or priority queue object needs to be instantiated, code such as the following is used:

Queue q = new ListQueue();
// ListQueue implements Queue
See also...
 Computer Science A & AB: Introduction of Java in 2003-2004
 Computer Science A: Quick Reference Guide

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