Java集合综述

最新推荐文章于 2025-08-09 15:58:26 发布

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1. 集合类和数组

（1）数组元素可以是基本数据类型也可以是对象，而集合里只能保存对象。

（2）数组创建之后长度是固定的不能改变，集合类创建后长度可以随着数据量的大小自动增长。

2. Java集合接口由两个接口派生：Collection和Map。

3.Collection接口是List、Set、Queue接口的父接口，常用方法如下：

Methods
修饰符与类型	方法与描述
`boolean`	`add(E e)` Ensures that this collection contains the specified element (optional operation).
`boolean`	`addAll(Collection<? extendsE> c)` Adds all of the elements in the specified collection to this collection (optional operation).
`void`	`clear()` Removes all of the elements from this collection (optional operation).
`boolean`	`contains(Object o)` Returns `true` if this collection contains the specified element.
`boolean`	`containsAll(Collection<?> c)` Returns `true` if this collection contains all of the elements in the specified collection.
`boolean`	`equals(Object o)` Compares the specified object with this collection for equality.
`int`	`hashCode()` Returns the hash code value for this collection.
`boolean`	`isEmpty()` Returns `true` if this collection contains no elements.
`Iterator<E>`	`iterator()` Returns an iterator over the elements in this collection.
`boolean`	`remove(Object o)` Removes a single instance of the specified element from this collection, if it is present (optional operation).
`boolean`	`removeAll(Collection<?> c)` Removes all of this collection's elements that are also contained in the specified collection (optional operation).
`boolean`	`retainAll(Collection<?> c)` Retains only the elements in this collection that are contained in the specified collection (optional operation).
`int`	`size()` Returns the number of elements in this collection.
`Object[]`	`toArray()` Returns an array containing all of the elements in this collection.
`<T> T[]`	`toArray(T[] a)` Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array

4.Collection遍历的两种方式：Iterator和foreach

Collection<String> col = new HashSet<String>();
		col.add("a");
		col.add("b");
		col.add("c");
		col.add("d");
		
		//Iterator遍历
		Iterator it = col.iterator();
		while(it.hasNext())
		{
			System.out.print(it.next());
		}
		System.out.println();
		
		//foreach 遍历
		for(String str:col)
		{
		System.out.print(str);	
		}