set集合

我就是我 2024-03-16 18:50 52阅读 0赞

**目录**

1，set集合的特点：

1.1，set集合添加的数据不可重复

1.2 hashset无序 Treeset有序

1.2.1set集合的遍历方法

1.2.2Treeset自定义对象无法排序，hashSet因为是无序所以会无规则遍历

1.2.3如何让Treeset集合进行排序（自然排序.比较器排序 ）

--------------------

## 1，set集合的特点： ##

### 1.1，set集合添加的数据不可重复 ###

public static void main(String[] args) {
        Set s = new HashSet();
        s.add("b");
        s.add("a");
        s.add("c");
        s.add("b");
        System.out.println(s);
    }

通过上一行代码输出的结果为：

![91161c8d7a004e4e9672a0d0143d2406.png][]

由此可以说明set集合里的数据不可重复。

但是若存放的数据为对象时:

public static void main(String [] args) {
    	
    	HashSet<Object> set =new HashSet<Object>();
    	set.add(new person("zs",12));
    	set.add(new person("ww",12));
    	set.add(new person("ls",12));
    	System.out.println(set.size());
    	set.add(new person("ww",12));
    	System.out.println(set.size());
    	
    }

运行此段代码的结果如图：

![6d3ecad2c5904966a301f6f45af626c6.png][]

由此可以说明但我们在set集合添加属性值一样的对象时，因为地址同所以可以存放进去，那我们该怎么解决？我们尝试用list集合去重原理试一下。

package com.xzs.set;
    
    import java.util.HashSet;
    import java.util.Set;
    
    public class demo1 {
    public static void main(String [] args) {
    	
    	HashSet<Object> set =new HashSet<Object>();
    	set.add(new person("zs",12));
    	set.add(new person("ww",12));
    	set.add(new person("ls",12));
    	System.out.println(set.size());
    	set.add(new person("ww",12));
    	System.out.println(set.size());
    	
    }
    
    }
    class person{
    	private String name;
    	private int 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;
    	}
    	public person(String name, int age) {
    		super();
    		this.name = name;
    		this.age = age;
    	}
    	public person() {
    		super();
    	}
    	@Override
    	public String toString() {
    		return "person [name=" + name + ", 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;
    		person other = (person) 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;
    	}
    	
    }

以上代码运行结果是

![3101d63e032b4de58af224da73d67b05.png][]

同样集合的长度还是3和4由此说明set集合与list集合判定的底层逻辑就不同

package com.xzs.set;
    
    import java.util.HashSet;
    import java.util.Set;
    
    public class demo1 {
    public static void main(String [] args) {
    	
    	HashSet<Object> set =new HashSet<Object>();
    	set.add(new person("zs",12));
    	set.add(new person("ww",12));
    	set.add(new person("ls",12));
    	System.out.println(set.size());
    	set.add(new person("ww",12));
    	System.out.println(set.size());
    	
    }
    
    }
    class person{
    	private String name;
    	private int 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;
    	}
    	public person(String name, int age) {
    		super();
    		this.name = name;
    		this.age = age;
    	}
    	public person() {
    		super();
    	}
    	@Override
    	public String toString() {
    		return "person [name=" + name + ", age=" + age + "]";
    	}
    	@Override
    	public int hashCode() {
    		System.out.println("hashcode被调用了");
    		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) {
    		System.out.println("equals被调用了");
    		if (this == obj)
    			return true;
    		if (obj == null)
    			return false;
    		if (getClass() != obj.getClass())
    			return false;
    		person other = (person) 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;
    	}
    	
    }

同样是上一行代码，这时候运行的结果为

![d1842ec0e9ae4bacb9736618af0f0fd8.png][]

由此可以说明，set集合在判定数据是先通过hascode，并且在上类代码中当我们的hashcode被注释的时候equlas，也不会被调用，所以set集合的判定是否为重复数组的原理是：“先来通过hashcode判定，才会进入equals判定”

### 1.2 hashset无序 Treeset有序 ###

要想判定set集合是否为有序的我们可以遍历他的元素即可

#### 1.2.1set集合的遍历方法 ####

1.为迭代器也就是图中的Iterator

2.增强for也就是foreach

public static void main(String[] args) {
            Set s = new HashSet();
            s.add("a");
            s.add("c");
            s.add("b");
            for (Object o : s) {
                System.out.println(o);
            }
            System.out.println("==============================");
    
            Iterator it = s.iterator();
            while (it.hasNext()) {
                System.out.println(it.next());
            }
        }

结果为：

![3218cdf52bfc4d1997f31f7ab6fbb4d4.png][]

证明 string 类型是可以自动排序的

#### 1.2.2Treeset自定义对象无法排序，hashSet因为是无序所以会无规则遍历 ####

package com.xzs.set;
    
    import java.util.HashSet;
    import java.util.Iterator;
    import java.util.Set;
    import java.util.TreeSet;
    
    public class demo1 {
    public static void main(String [] args) {
    	
    	TreeSet<Object> set =new TreeSet<Object>();
    	set.add(new person("zs",3,12));
    	set.add(new person("ww",6,92));
    	set.add(new person("ls",1,17));
    	System.out.println(set.size());
    	for (Object object : set) {
    		System.out.println(object);
    	}
    	
    }
    
    }
    class person{
    	private String name;
    	private int level;
    	private int age;
    	public int getLevel() {
    		return level;
    	}
    	public void setLevel(int level) {
    		this.level = level;
    	}
    	
    	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;
    	}
    	public person(String name, int age) {
    		super();
    		this.name = name;
    		this.age = age;
    	}
    	
    	@Override
    	public String toString() {
    		return "person [name=" + name + ", level=" + level + ", age=" + age + "]";
    	}
    	public person(String name, int level, int age) {
    		super();
    		this.name = name;
    		this.level = level;
    		this.age = age;
    	}
    	public person() {
    		super();
    	}
    	@Override
    	public int hashCode() {
    		final int prime = 31;
    		int result = 1;
    		result = prime * result + age;
    		result = prime * result + level;
    		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;
    		person other = (person) obj;
    		if (age != other.age)
    			return false;
    		if (level != other.level)
    			return false;
    		if (name == null) {
    			if (other.name != null)
    				return false;
    		} else if (!name.equals(other.name))
    			return false;
    		return true;
    	}
    
    	
    
    	
    }

结果为：会出现数据转化异常

![04ffb9708cbb441191e41d54829fae77.png][]

#### 1.2.3如何让Treeset集合进行排序（自然排序.比较器排序 ） ####

package com.xzs.set;
    
    import java.util.HashSet;
    import java.util.Iterator;
    import java.util.Objects;
    import java.util.Set;
    import java.util.TreeSet;
    
    public class demo1 {
    	public static void main(String[] args) {
            Set s = new TreeSet();
           s.add(new Student("zs",17));
           s.add(new Student("ls",19));
           s.add(new Student("ww",18));
            System.out.println("目前集合容器中的元素："+s);
    
        }
    }
    class Student implements Comparable{
        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 boolean equals(Object o) {
            System.out.println("调用了equals方法。。。");
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Student student = (Student) o;
            return age == student.age && name.equals(student.name);
        }
    
        @Override
        public int hashCode() {
            System.out.println("调用了hashCode方法。。。");
            return Objects.hash(name, age);
        }
    
    
    
        @Override
        public String toString() {
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    
        @Override
        public int compareTo(Object o) {
            Student student = (Student) o;
            return this.age - student.age;
        }
    }

结果为：

![43c9c843e94a49c9b72f62cc69667808.png][]

当然我们也可以用TreeSet构造器使用实现java.util.Comparator的匿名内部类

如

package com.xzs.set;
    
    import java.util.Comparator;
    import java.util.HashSet;
    import java.util.Iterator;
    import java.util.Objects;
    import java.util.Set;
    import java.util.TreeSet;
    
    public class demo1 {
    	public static void main(String[] args) {
    		TreeSet s=new TreeSet(new Comparator() {
    			public int compare(Object o1, Object o2) {
                    System.out.println("调用了compare方法。。。");
                    Student s1 = (Student) o1;
                    Student s2 = (Student) o2;
                    if (s1.getAge()-s2.getAge() == 0)
                        return s1.getName().compareTo(s2.getName());
                    return s1.getAge()-s2.getAge();
                }
    		});
            s.add(new Student("zs",16));
            s.add(new Student("ls",17));
            s.add(new Student("zs",17));
            s.add(new Student("ww",18));
            System.out.println("目前集合容器中的元素："+s);
        }
    		
    }
    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 boolean equals(Object o) {
            System.out.println("调用了equals方法。。。");
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Student student = (Student) o;
            return age == student.age && name.equals(student.name);
        }
    
        @Override
        public int hashCode() {
            System.out.println("调用了hashCode方法。。。");
            return Objects.hash(name, age);
        }
    
    
    
        @Override
        public String toString() {
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    
        
       
    }

得到的结果为：

![81c13db714c740a69e0216e00d7cabc8.png][]

[91161c8d7a004e4e9672a0d0143d2406.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/082b7de05024404da247d582ca654aec.png
[6d3ecad2c5904966a301f6f45af626c6.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/d43bb56ad18747e2811f8117501393b7.png
[3101d63e032b4de58af224da73d67b05.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/97d117a491a74b9cb4a953a6523caf70.png
[d1842ec0e9ae4bacb9736618af0f0fd8.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/0fbbc0788a654e7c9df21fb76e3c0b74.png
[3218cdf52bfc4d1997f31f7ab6fbb4d4.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/dd1e6e65c8014fbc9fcb9bd91afb4efb.png
[04ffb9708cbb441191e41d54829fae77.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/891d88e996354059a3c8b02eaea03936.png
[43c9c843e94a49c9b72f62cc69667808.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/15221b8def13412db8efbe3c19f9c94a.png
[81c13db714c740a69e0216e00d7cabc8.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/6d45a413e1184b2985716fa1a8e9ebba.png