第三次學JAVA再學不好就喫翔(part81)--去除ArrayList中重複元素

學習筆記，僅供參考

因爲我突然懶了，所以這個Blog以代碼爲主，解釋爲輔

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集合

去除ArrayList中重複的字符串元素

package com.guiyang.object;

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

@SuppressWarnings({ "rawtypes", "unchecked" })
public class Demo1_ArrayList {

	public static void main(String[] args) {
		ArrayList alist = new ArrayList();
		alist.add("a");
		alist.add("a");
		alist.add("a");
		alist.add("b");
		alist.add("b");
		alist.add("c");
		
		ArrayList newlist = getSingle(alist);
		System.out.println(newlist);
		

	}
	
	public static ArrayList getSingle(ArrayList list) {
		ArrayList newlist = new ArrayList();
		
		Iterator iterator = list.iterator();
		
		while (iterator.hasNext()) {
			Object object = iterator.next();
			if (!newlist.contains(object)) {
				newlist.add(object);
			}
			
		}
		return newlist;
	}

}

輸出：

[a, b, c]

去除ArrayList中重複的自定義對象元素

注意，contains方法判斷集合中是否包含某個元素，底層依賴的是equals方法。

所以，在進行定義對象的比較時，我們需要改寫自定義類的equals方法.

自定義Person類：

package com.guiyang.bean;

public class Person {
	private String name;
	private int age;
	public Person() {
		super();
		
	}
	public Person(String name, int age) {
		super();
		this.name = name;
		this.age = age;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + "]";
	}

	@Override
	public boolean equals(Object obj) {
		Person p = (Person)obj;
		return this.name.equals(p.name) && this.age == p.age;
	}
	
}

Java:

package com.guiyang.restudy3;
import java.util.ArrayList;
import java.util.Iterator;

import com.guiyang.bean.Person;

@SuppressWarnings({"rawtypes", "unchecked"})
public class D2ArrayListRepeat {

	public static void main(String[] args) {
		ArrayList list = new ArrayList();	//創建集合對象
		list.add(new Person("小白", 23));
		list.add(new Person("小白", 23));
		list.add(new Person("大黃", 24));
		list.add(new Person("大黃", 24));
		list.add(new Person("王子", 24));
		
		ArrayList newList = getSingle(list);	//調用方法去除重複
		System.out.println(newList);

	}

	public static ArrayList getSingle(ArrayList list) {
		ArrayList newList = new ArrayList<>();		//1,創建新集合
		Iterator it = list.iterator();	//2,根據傳入的集合(老集合)獲取迭代器
		
		while(it.hasNext()) {		   //3,遍歷老集合
			Object obj = it.next();		//記錄住每一個元素
			if(!newList.contains(obj)) {//如果新集合中不包含老集合中的元素
				newList.add(obj);	    //將該元素添加
			}
		}
		
		return newList;
	}

}

輸出：

[Person [name=小白, age=23], Person [name=大黃, age=24], Person [name=王子, age=24]]

同樣，remove方法移除集合中的某個元素時，底層依賴的還是equals方法。

package com.guiyang.restudy3;
import java.util.ArrayList;
import java.util.Iterator;

import com.guiyang.bean.Person;

@SuppressWarnings({"rawtypes", "unchecked"})
public class D2ArrayListRepeat {

	public static void main(String[] args) {
		ArrayList list = new ArrayList();		//創建集合對象
		list.add(new Person("小白", 23));
		list.add(new Person("小白", 23));
		list.add(new Person("大黃", 24));
		list.add(new Person("大黃", 24));
		list.add(new Person("王子", 24));
		
		list.remove(new Person("王子", 24));
		System.out.println(list);
	}

	public static ArrayList getSingle(ArrayList list) {
		ArrayList newList = new ArrayList<>();	//1,創建新集合
		Iterator it = list.iterator();	//2,根據傳入的集合(老集合)獲取迭代器
		
		while(it.hasNext()) {			 //3,遍歷老集合
			Object obj = it.next();		 //記錄住每一個元素
			if(!newList.contains(obj)) { //如果新集合中不包含老集合中的元素
				newList.add(obj);		 //將該元素添加
			}
		}
		return newList;
	}
}

輸出：

[Person [name=小白, age=23], Person [name=小白, age=23], Person [name=大黃, age=24], Person [name=大黃, age=24]]

LinkedList的特有功能

package com.guiyang.restudy3;

import java.util.LinkedList;

@SuppressWarnings({ "rawtypes", "unchecked" })
public class D1Linkedlist {

	public static void main(String[] args) {
		LinkedList list = new LinkedList();
		list.addFirst("a");
		list.addFirst("b");
		list.addFirst("c");
		list.addFirst("d");
		list.addLast("e");
		list.addLast("f");
		
		System.out.println(list.getFirst());
		System.out.println(list.getLast());
		System.out.println(list.removeFirst());
		System.out.println(list.removeLast());
		System.out.println("---------");
		System.out.println(list.get(0));
		System.out.println(list);
	}

}

輸出：

d
f
d
f
---------
c
[c, b, a, e]