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Home Java Javagetting Started How to create a unique collection in java?

How to create a unique collection in java?

Feb 03, 2020 am 10:23 AM
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How to create a unique collection in java?

#How to create a unique collection in Java?

There are many ways to create unique collections in Java. Below we introduce four common methods for creating unique collections in Java.

Method 1: You need an array to store the deduplicated elements, and then two layers of loops. The outer layer traverses the original array, and the content is judged one by one whether it matches the following elements. Repeat, and then pull it out again and store it in a new array.

    public static Object[] ifRepeat(Object[] arr){  
        //用來記錄去除重復(fù)之后的數(shù)組長度和給臨時數(shù)組作為下標(biāo)索引  
        int t = 0;  
        //臨時數(shù)組  
        Object[] tempArr = new Object[arr.length];  
        //遍歷原數(shù)組  
        for(int i = 0; i < arr.length; i++){  
            //聲明一個標(biāo)記,并每次重置  
            boolean isTrue = true;  
            //內(nèi)層循環(huán)將原數(shù)組的元素逐個對比  
            for(int j=i+1;j<arr.length;j++){  
                //如果發(fā)現(xiàn)有重復(fù)元素,改變標(biāo)記狀態(tài)并結(jié)束當(dāng)次內(nèi)層循環(huán)  
                if(arr[i]==arr[j]){  
                    isTrue = false;  
                    break;  
                }  
            }  
            //判斷標(biāo)記是否被改變,如果沒被改變就是沒有重復(fù)元素  
            if(isTrue){  
                //沒有元素就將原數(shù)組的元素賦給臨時數(shù)組  
                tempArr[t] = arr[i];  
                //走到這里證明當(dāng)前元素沒有重復(fù),那么記錄自增  
                t++;  
            }  
        }  
        //聲明需要返回的數(shù)組,這個才是去重后的數(shù)組  
        Object[]  newArr = new Object[t];  
        //用arraycopy方法將剛才去重的數(shù)組拷貝到新數(shù)組并返回  
        System.arraycopy(tempArr,0,newArr,0,t);  
        return newArr;  
    }

Method 2: Just create a collection, then traverse the array and put it into the collection one by one. Just use the contains() method to determine whether the element already exists in the collection before putting it in. , and then use toArray to convert it into an array.

   public static void ifRepeat2(Object[] arr){  
        //創(chuàng)建一個集合  
        List list = new ArrayList();  
        //遍歷數(shù)組往集合里存元素  
        for(int i=0;i<arr.length;i++){  
            //如果集合里面沒有相同的元素才往里存  
            if(!list.contains(arr[i])){  
                list.add(arr[i]);  
            }  
        }  
          
        //toArray()方法會返回一個包含集合所有元素的Object類型數(shù)組  
        Object[] newArr = list.toArray();  
        //遍歷輸出一下測試是否有效  
        for(int i=0;i<newArr.length;i++){  
            System.out.println(" "+newArr[i]);  
        }  
  
    }

Method 3. The simplest method is to use the unordered and non-repeatable characteristics of the Set collection to filter elements.

public static Object[] ifRepeat3(Object[] arr){  
        //實例化一個set集合  
        Set set = new HashSet();  
        //遍歷數(shù)組并存入集合,如果元素已存在則不會重復(fù)存入  
        for (int i = 0; i < arr.length; i++) {  
            set.add(arr[i]);  
        }  
        //返回Set集合的數(shù)組形式  
        return set.toArray();  
    }

Method 4. Hash set of linked list: in order and not repeated.

 public static void ifRepeat4(Object[] arr){  
          
        LinkedHashSet<Object> haoma = new LinkedHashSet<Object>();  
        for (int i = 0; i < arr.length; i++) {  
            haoma.add(arr[i]);  
        }  
          
        // 創(chuàng)建迭代器  
        Iterator<Object> iterator = haoma.iterator();  
        int a = 0;  
        // 迭代集合  
        while (iterator.hasNext()) { // true  
            Object c = iterator.next();  
              
            System.out.println(c);  
        }  
    }

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