JAVA------Collection Overview---Collection Common Methods

1. The characteristics of the collection :

• Provide a storage model with variable storage space, and the stored data capacity can be changed at any time
• The collection stores a reference type, so the packaging class should be used when storing, for example, Integer should be used to store int

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2. Collection classification :

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3. Create a Collection collection object :

Because Collection is an interface, objects should be created in a polymorphic manner

Collection<String> c=new ArrayList<String>();

Example:

package Collection;

import java.util.*;
import java.util.concurrent.ArrayBlockingQueue;

public class CollectionDemo01 {
    
    
	public static void main(String[] args) {
    
    
		//创建Collection集合的对象
		Collection<String> c=new ArrayList<String>();
		
		//添加元素 boolean add(E e)
		c.add("hello");
		c.add("world");
		c.add("java");
		//ArrayList重写了toString方法	
		System.out.println(c);
		
	}

}

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4. Collection commonly used methods:

 boolean add(E e)                添加元素
 boolean remove(Object o)		 从集合中移除指定元素
 void clear()					 清空集合中的元素
 boolean contains(Object o)		 判断集合中是否存在指定元素
 boolean isEmpty()				 判断集合是否为空
 int size()						 集合的长度，也就是集合中元素的个数

Example:

package Collection;

import java.util.ArrayList;
import java.util.Collection;

public class CollectionDemo02 {
    
    
	public static void main(String[] args) {
    
    
		//创建Collection集合的对象
		Collection<String> c=new ArrayList<String>();
		
		//add永远返回true
		System.out.println(c.add("hello"));
		System.out.println(c.add("hello"));
		System.out.println(c.add("world"));
		
		System.out.println(c.remove("wold"));
		
		System.out.println(c);
	}
}

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5. Iterator: collection-specific traversal method

• Iterator iterator returns the iterator of the elements in the collection, obtained by the iterator() method of the collection
• boolean hasNext(): returns true if the iterator has more elements
• E next(): returns the next element in the iterator

Example:

package Collection;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class CollectionDemo03 {
    
    
	public static void main(String[] args) {
    
    
		//创建Collection集合的对象
		Collection<String> c=new ArrayList<String>();
		
		//add永远返回true
		c.add("hello");
		c.add("world");
		c.add("java");

		Iterator<String> it=c.iterator();
		while(it.hasNext()){
    
    //如果迭代器具有更多元素，返回
			//System.out.println(it.next());
			String s=it.next();//返回迭代器下一个元素
			System.out.println(s);
		}
			
	}
}