Java集合框架--List去重

一、Java List 类
二、Java List 排序
三、Java List 遍历
四、Java List 去重
五、Java List 转Array

四、Java List 去重

• 方法一： 双循环去重

//先遍历原数组array，然后遍历去重过后的result集，通过每个数组的元素和结果集中的元素进行比对
//若相同则break。若不相同，则存入result集。
String[] array = {"a","b","c","c","d","c","e","a"};  
List<String> result = new ArrayList<>();  
boolean flag;  
for(int i=0; i<array.length; ++i){  
    flag = false;  
    for(int j=0; j<result.size(); ++j){  
        if( array[i].equals(result.get(j)) ){  
            flag = true;  
            break;  
        }
    } 
    if(!flag) result.add(array[i]);  
}  
String[] arrayResult = (String[]) result.toArray(new String[result.size()]);  
System.out.println(Arrays.toString(arrayResult));  

• 方法二 indexOf()去重

//用indexOf()方法判单结果集list2是否存在当前元素
String[] array = {"a","b","c","c","d","e","e","e","a"};
List<String> list2 = new ArrayList<>();
list2.add(array[0]);
for(int i=1; i<array.length; ++i) {
	if ( list2.toString().indexOf( array[i] ) == -1 ) list2.add(array[i]);
}
String[] arrayResult = (String[]) list2.toArray(new String[list2.size()]);  
System.out.println(Arrays.toString(arrayResult));  

• 方法三 嵌套循环去重

String[] array = {"a","b","c","c","d","e","e","e","a"};  
List<String> list3 = new ArrayList<>();
for(int i=0; i<array.length; ++i ) {
	for(int j=i+1; j<array.length; ++j) {
		if ( array[i] == array[j] )  j = ++i;
	}
	list3.add(array[i]);
}
String[] arrayResult = (String[]) list3.toArray(new String[list3.size()]);  
System.out.println(Arrays.toString(arrayResult));

• 方法四 sort排序去重

String[] array = {"a","b","c","c","d","e","e","e","a"};  
Arrays.sort(array);  
List<String> list = new ArrayList<>();  
list.add(array[0]);  
for(int i=1;i<array.length;i++){  
    if(!array[i].equals(list.get(list.size()-1))){  
       list.add(array[i]);  
    }  
}
String[] arrayResult = (String[]) list.toArray(new String[list.size()]);  
System.out.println(Arrays.toString(arrayResult));

• 方法五 set方法去重

String[] array = {"a","b","c","c","d","e","e","e","a"};  
Set<String> set = new HashSet<>();  
for(int i=0;i<array.length;i++){  
    set.add(array[i]);  
}  
String[] arrayResult = (String[]) set.toArray(new String[set.size()]);  
System.out.println(Arrays.toString(arrayResult));  

• 方法六 Iterator遍历，remove方法移除去重

 List<String> list=new ArrayList<>();
 list.add("a");	list.add("b");	list.add("a");	list.add("c");
 list.add("b");	list.add("d");
 
 List<String> listTemp= new ArrayList<>();  
 Iterator<String> it=list.iterator();  
 while(it.hasNext()){  
	 String a = it.next();  
	 if(listTemp.contains(a))	it.remove(); 
	 else	listTemp.add(a);  
 }  
 for(String i:list)	System.out.println(i);