Java中List去重的四种方法

迷南。 2023-10-08 12:00 27阅读 0赞

package com.lxz.test;
    
    import java.util.ArrayList;
    import java.util.HashSet;
    import java.util.Iterator;
    import java.util.List;
    import java.util.Set;
    
    /**
     * description: List去重
     * date: 2018年2月10日
     * author: www.luxinzhi.com
     */
    public class ListRemoveDuplicate {
    
    	// Java中去重的方法有很多，常用的方法主要有下面4种
    	// 1. 循环list中的所有元素然后删除重复元素
    	@SuppressWarnings("rawtypes")
    	public static List removeDuplicate1(List list) {
    		for (int i = 0; i < list.size() - 1; i++) {
    			for (int j = list.size() - 1; j > i; j--) {
    				if (list.get(j).equals(list.get(i))) {
    					list.remove(j);
    				}
    			}
    		}
    		return list;
    	}
    
    	// 2. 通过HashSet踢除重复元素
    	@SuppressWarnings({ "unchecked", "rawtypes" })
    	public static List removeDuplicate2(List list) {
    		HashSet set = new HashSet(list);
    		// 保持原有顺序
    		// HashSet set = new LinkedHashSet(list);
    list.clear();
    		list.addAll(set);
    		return list;
    	}
    
    	// 3. 删除ArrayList中重复元素，保持原有顺序
    	@SuppressWarnings({ "unchecked", "rawtypes" })
    	public static List removeDuplicateWithOrder3(List list) {
    		Set set = new HashSet();
    		List newList = new ArrayList();
    		for (Iterator iter = list.iterator(); iter.hasNext();) {
    			Object element = iter.next();
    			if (set.add(element)) {
    				newList.add(element);
    			}
    		}
    		list.clear();
    		list.addAll(newList);
    		return list;
    	}
    
    	// 4. 把list里的对象遍历一遍，用list.contain()，如果不存在就放入到另外一个list集合中
    	@SuppressWarnings({ "unchecked", "rawtypes" })
    	public static List removeDuplicate4(List list) {
    		List newList = new ArrayList();
    		for (int i = 0; i < list.size(); i++) {
    			if (!newList.contains(list.get(i))) {
    				newList.add(list.get(i));
    			}
    		}
    		return newList;
    	}
    
    	@SuppressWarnings("rawtypes")
    	public static void main(String[] args) {
    		List list = new ArrayList<>();
    		list.add("aaa");
    		list.add("ccc");
    		list.add("bbb");
    		list.add("ccc");
    		list.add("ddd");
    		list.add("aaa");
    
    		List list1 = removeDuplicate1(list);
    		List list2 = removeDuplicate2(list);
    		List list3 = removeDuplicateWithOrder3(list);
    		List list4 = removeDuplicate4(list);
    
    		System.out.println("--------1--------");
    		for (int i = 0; i < list1.size(); i++) {
    			System.out.println(list1.get(i));
    		}
    		System.out.println("--------2--------");
    		for (int i = 0; i < list2.size(); i++) {
    			System.out.println(list2.get(i));
    		}
    		System.out.println("--------3--------");
    		for (int i = 0; i < list3.size(); i++) {
    			System.out.println(list3.get(i));
    		}
    		System.out.println("--------4--------");
    		for (int i = 0; i < list4.size(); i++) {
    			System.out.println(list4.get(i));
    		}
    
    	}
    
    }

输出结果
    
    --------1--------
    aaa
    ccc
    bbb
    ddd
    --------2--------
    aaa
    ccc
    bbb
    ddd
    --------3--------
    aaa
    ccc
    bbb
    ddd
    --------4--------
    aaa
    ccc
    bbb
    ddd

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