Java List实体类去重

最新推荐文章于 2025-07-01 10:36:06 发布

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#java #List #排序 #去重 #实体类

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本文介绍了如何在Java中使用List特性结合实体类进行数据去重。通过对比List和Set的特点，强调Set的不可重复性，指出尽管Set没有特定的插入顺序，但元素位置由HashCode决定。示例中提到了创建实体类并利用Set进行去重的操作。

List特点：元素有放入顺序，元素可重复

Map特点：元素按键值对存储，无放入顺序

Set特点：元素无放入顺序，元素不可重复（注意：元素虽然无放入顺序，但是元素在set中的位置是有该元素的HashCode决定的，其位置其实是固定的）

新建一个实体类

public class User {
	private String id;
	private String name;
	private String age;
	private String address;

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAge() {
		return age;
	}

	public void setAge(String age) {
		this.age = age;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((id == null) ? 0 : id.hashCode());
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		result = prime * result + ((age == null) ? 0 : age.hashCode());
		result = prime * result + ((address == null) ? 0 : address.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj) {
			return true;
		}
		if (obj == null) {
			return false;
		}
		if (getClass() != obj.getClass()) {
			return false;
		}
		User other = (User) obj;
		if (id == null) {
			if (other.id != null) {
				return false;
			}
		} else if (!id.equals(other.id)) {
			return false;
		}
		if (name == null) {
			if (other.name != null) {
				return false;
			}
		} else if (!name.equals(other.name)) {
			return false;
		}
		if (age == null) {
			if (other.age != null) {
				return false;
			}
		} else if (!age.equals(other.age)) {
			return false;
		}
		if (address == null) {
			if (other.address != null) {
				return false;
			}
		} else if (!address.equals(other.address)) {
			return false;
		}
		return true;
	}
}

调用即可

	private static List<User> removeListDuplicateObject(List<User> list) { 
		System.out.println(Arrays.toString(list.toArray())); 
		Set<User> set = new HashSet<User>(); 
		set.addAll(list); 
		System.out.println(Arrays.toString(set.toArray()));
		List<User> listnewList = new ArrayList<User>(set);
		return listnewList;
		}

附上一个按某个字段排序功能

	@Override
	public int compareTo(DBBakPolicyDetail arg0) {
		if(this.getDbName() == null && arg0.getDbName() == null){
			return 0;
		}else if(this.getDbName() == null && arg0.getDbName() != null){
			return 1;
		}else if(this.getDbName() != null && arg0.getDbName() == null){
			return -1;
		}else {
			return this.getDbName().compareTo(arg0.getDbName());
		}
	}

<span style="font-family: Helvetica, Tahoma, Arial, sans-serif; font-size: 14px; line-height: 25.200000762939453px;">List特点：元素有放入顺序，元素可重复 </span><br style="font-family: Helvetica, Tahoma, Arial, sans-serif; font-size: 14px; line-height: 25.200000762939453px;" /><span style="font-family: Helvetica, Tahoma, Arial, sans-serif; font-size: 14px; line-height: 25.200000762939453px;">Map特点：元素按键值对存储，无放入顺序 </span><br style="font-family: Helvetica, Tahoma, Arial, sans-serif; font-size: 14px; line-height: 25.200000762939453px;" /><p><span style="font-family: Helvetica, Tahoma, Arial, sans-serif; font-size: 14px; line-height: 25.200000762939453px;">Set特点：元素无放入顺序，元素不可重复（注意：元素虽然无放入顺序，但是元素在set中的位置是有该元素的HashCode决定的，其位置其实是固定的） </span></p><p><span style="font-family: Helvetica, Tahoma, Arial, sans-serif;"><span style="font-size: 14px; line-height: 25.200000762939453px;">新建一个实体类</span></span></p>

public class User {
	private String id;
	private String name;
	private String age;
	private String address;

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAge() {
		return age;
	}

	public void setAge(String age) {
		this.age = age;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((id == null) ? 0 : id.hashCode());
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		result = prime * result + ((age == null) ? 0 : age.hashCode());
		result = prime * result + ((address == null) ? 0 : address.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj) {
			return true;
		}
		if (obj == null) {
			return false;
		}
		if (getClass() != obj.getClass()) {
			return false;
		}
		User other = (User) obj;
		if (id == null) {
			if (other.id != null) {
				return false;
			}
		} else if (!id.equals(other.id)) {
			return false;
		}
		if (name == null) {
			if (other.name != null) {
				return false;
			}
		} else if (!name.equals(other.name)) {
			return false;
		}
		if (age == null) {
			if (other.age != null) {
				return false;
			}
		} else if (!age.equals(other.age)) {
			return false;
		}
		if (address == null) {
			if (other.address != null) {
				return false;
			}
		} else if (!address.equals(other.address)) {
			return false;
		}
		return true;
	}
}

之后调用即可

	private static List<User> removeListDuplicateObject(List<User> list) { 
		System.out.println(Arrays.toString(list.toArray())); 
		Set<User> set = new HashSet<User>(); 
		set.addAll(list); 
		System.out.println(Arrays.toString(set.toArray()));
		List<User> listnewList = new ArrayList<User>(set);
		return listnewList;
		}

附上一个按某个字段排序的功能:

	@Override
	public int compareTo(DBBakPolicyDetail arg0) {
		if(this.getDbName() == null && arg0.getDbName() == null){
			return 0;
		}else if(this.getDbName() == null && arg0.getDbName() != null){
			return 1;
		}else if(this.getDbName() != null && arg0.getDbName() == null){
			return -1;
		}else {
			return this.getDbName().compareTo(arg0.getDbName());
		}
	}