java中Set用法

set 與list相比，是無順序的，去除重複項（重寫Hashset和equals方法後）。

package my.lists;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Scanner;
import java.util.Set;
import java.util.List;
public class Student{
	private String name;
	private int age;
	public Student(String name,int age) {
		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 "Student [name=" + name + ", age=" + age + "]";
	}


	public static void main(String[] args) {
		Set<Student> stuL=new HashSet<Student>();
		Student stu1=new Student("a橘子",1);
		Student stu2=new Student("b香蕉",2);
		Student stu3=new Student("c蘋果",3);
		Student stu4=new Student("d草莓",4);
		Student stu5=new Student("e橙子",5);
		Student stu6=new Student("f柚子",6);
		Student stu7=new Student("g梨",7);
		Student stu8=new Student("h葡萄",8);
		stuL.add(stu1);
		stuL.add(stu2);
		stuL.add(stu3);
		stuL.add(stu4);
		stuL.add(stu5);
		stuL.add(stu6);
		stuL.add(stu7);
		stuL.add(stu8);
		Iterator<Student> iter=stuL.iterator();
		while(iter.hasNext()) {
			System.out.println(iter.next());
		}
		
	}
}

 

hashSet去除重複是調用對象的HashCode 和equals方法。

package my.lists;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Scanner;
import java.util.Set;
import java.util.List;
public class Student{
	private String name;
	private int age;
	public Student(String name,int age) {
		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 int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + age;
		result = prime * result + ((name == null) ? 0 : name.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;
		Student other = (Student) obj;
		if (age != other.age)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}


	@Override
	public String toString() {
		return "Student [name=" + name + ", age=" + age + "]";
	}
	
	public static void main(String[] args) {
		Set<Student> stuL=new HashSet<Student>();
		Student stu1=new Student("a橘子",1);
		Student stu2=new Student("b香蕉",2);
		Student stu3=new Student("c蘋果",3);
		Student stu9=new Student("c蘋果",3);
		Student stu4=new Student("d草莓",4);
		Student stu5=new Student("e橙子",5);
		Student stu6=new Student("f柚子",6);
		Student stu7=new Student("g梨",7);
		Student stu8=new Student("h葡萄",8);
		stuL.add(stu1);
		stuL.add(stu2);
		stuL.add(stu3);
		stuL.add(stu4);
		stuL.add(stu5);
		stuL.add(stu6);
		stuL.add(stu7);
		stuL.add(stu8);
		stuL.add(stu9);
		Iterator<Student> iter=stuL.iterator();
		while(iter.hasNext()) {
			System.out.println(iter.next());
		}
		
	}



}

運行的結果是：

 如果不重寫equals方法，hashCode方法，則可以存在相同的對象。