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Java Dictionary

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Java Dictionary
list.remove() / clear() / size() / isEmpty()

list.remove() / clear() / size() / isEmpty()

Methods for removing elements from a list, clearing the entire list, and checking the number of elements or whether the list is empty. These are essential basic operations for managing and inspecting list state.

Syntax

// Removes the element at the specified index.
list.remove(int index);

// Removes the first element equal to the specified object.
list.remove(Object o);

// Removes all elements from the list.
list.clear();

// Returns the number of elements in the list.
list.size();

// Returns whether the list is empty.
list.isEmpty();

Method List

Method	Description
remove(int index)	Removes and returns the element at the specified index. Elements after it are shifted down by one.
remove(Object o)	Removes the first element equal to the specified object (determined by `equals()`). Returns `true` if an element was removed.
clear()	Removes all elements from the list, leaving it empty.
size()	Returns the number of elements contained in the list.
isEmpty()	Returns `true` if the list is empty (has zero elements), or `false` otherwise.

Sample Code

import java.util.ArrayList;

ArrayList<String> list = new ArrayList<>();
list.add("apple");
list.add("banana");
list.add("cherry");
list.add("banana");
System.out.println(list); // Prints "[apple, banana, cherry, banana]"

// Remove by index.
list.remove(0); // Removes "apple" at index 0.
System.out.println(list); // Prints "[banana, cherry, banana]"

// Remove by object (only the first matching element).
list.remove("banana");
System.out.println(list); // Prints "[cherry, banana]"

// Check the size with size().
System.out.println(list.size()); // Prints "2"

// Check whether the list is empty with isEmpty().
System.out.println(list.isEmpty()); // Prints "false"

// Clear the list with clear().
list.clear();
System.out.println(list);         // Prints "[]"
System.out.println(list.isEmpty()); // Prints "true"

// Note the difference between remove(int) and remove(Object) with an Integer list.
ArrayList<Integer> nums = new ArrayList<>(java.util.Arrays.asList(10, 20, 30));
nums.remove(0);                // Removes the element at index 0 (value 10).
System.out.println(nums);      // Prints "[20, 30]"
nums.remove(Integer.valueOf(20)); // Removes the element with value 20.
System.out.println(nums);      // Prints "[30]"

Notes

remove() is overloaded: when the argument is of type int, it removes by index; when it is of type Object, it removes by value. With an ArrayList<Integer>, writing remove(20) attempts to remove the element at index 20, not the value 20. To remove by value, use remove(Integer.valueOf(20)) to explicitly wrap the value.

Modifying a list while iterating over it can throw a ConcurrentModificationException. To safely remove elements inside a loop, use the Iterator's remove() method, or removeIf() available in Java 8 and later.

To add or retrieve elements, see add() / get(). To search for elements, see contains() / indexOf().

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