Set interface

Relationship

Hashset Common methods

1.add(Object obj)：

effect ：

towards Set Add elements to the collection .

however , Adding duplicate data is not allowed .

because HashMap Of key Repetition is not allowed, so HashSet The added elements are not allowed to be repeated

HashSet add The essence of the method is map Global variable called put Method , Save the data to key.

notes ： It does not guarantee set Order of iteration ; In particular, it does not guarantee that the order is permanent .

example ：

package second;
import java.util.HashMap;
import java.util.HashSet;
public class Test {
    
	public static void main(String [] args) {
    
		HashSet<String> set =new HashSet<String>();
		set.add("ufdhu");
		set.add("hwsfihojnckfh");
		for(String name:set) {
    
			System.out.println(name);
		}
	}
}

result ：

ufdhu
hwsfihojnckfh

If repeat ：
example ：

package second;
import java.util.HashMap;
import java.util.HashSet;
public class Test {
    
	public static void main(String [] args) {
    
		HashSet<String> set =new HashSet<String>();
		set.add("ufdhu");
		set.add("hwsfihojnckfh");
		set.add("hwsfihojnckfh");
		System.out.println(set.size());
		for(String name:set) {
    
			System.out.println(name);
		}
	}
}

result ：

2
ufdhu
hwsfihojnckfh

2.size() ：

effect ：

return Set The number of elements in the collection

example ：

package second;
import java.util.HashMap;
import java.util.HashSet;
public class Test {
    
	public static void main(String [] args) {
    
		HashSet<String> set =new HashSet<String>();
		set.add("ufdhu");
		set.add("hwsfihojnckfh");
		System.out.println(set.size());
		for(String name:set) {
    
			System.out.println(name);
		}
	}
}

result ：

2
ufdhu
hwsfihojnckfh

3.remove(Object obj) ：

effect ：

Delete Set The elements in the collection , Delete successful return true, Otherwise return to false.

example ：

package second;
import java.util.HashMap;
import java.util.HashSet;
public class Test {
    
	public static void main(String [] args) {
    
		HashSet<String> set =new HashSet<String>();
		set.add("ufdhu");
		set.add("hwsfihojnckfh");
		System.out.println(set.size());
		for(String name:set) {
    
			System.out.println(name);
		}
		boolean flag1=set.remove("fdfsfs");
		System.out.println(flag1);
		boolean flag2=set.remove("ufdhu");
		System.out.println(flag2);
	}
}

result ：

2
ufdhu
hwsfihojnckfh
false
true

4.isEmpty() ：

effect ：

If Set No elements , Then return to true , Otherwise return to false.

example ：

package second;
import java.util.HashMap;
import java.util.HashSet;
public class Test {
    
	public static void main(String [] args) {
    
		HashSet<String> set =new HashSet<String>();
		set.add("ufdhu");
		set.add("hwsfihojnckfh");
		System.out.println(set.isEmpty());
		boolean flag1=set.remove("hwsfihojnckfh");
		boolean flag2=set.remove("ufdhu");
		System.out.println(set.isEmpty());
	}
}

result ：

false
true

5.clear() ：

effect ：

To move in Set All elements in .

example ：

package second;
import java.util.HashMap;
import java.util.HashSet;
public class Test {
    
	public static void main(String [] args) {
    
		HashSet<String> set =new HashSet<String>();
		set.add("ufdhu");
		set.add("hwsfihojnckfh");
		System.out.println(set.isEmpty());
		set.clear();
		System.out.println(set.isEmpty());
	}
}

result ：

false
true

6.iterator() ：

effect ：

Back here Set Iterators that iterate over elements in

example ：

package second;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
public class Test {
    
	public static void main(String [] args) {
    
		HashSet<String> set =new HashSet<String>();
		set.add("ufdhu");
		set.add("hwsfihojnckfh");
		System.out.println(set.isEmpty());		
		Iterator<String> iterator =set.iterator();
		while(iterator.hasNext()) {
    
			System.out.println(iterator.next());
		}
	}
}

result ：

false
ufdhu
hwsfihojnckfh

7.contains(Object o)：

effect ：

Determine whether the set contains obj Elements .
If Set Contains the specified elements , Then return to true, Otherwise return to false

example ：

package second;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
public class Test {
    
	public static void main(String [] args) {
    
		HashSet<String> set =new HashSet<String>();
		set.add("ufdhu");
		set.add("hwsfihojnckfh");
		System.out.println(set.isEmpty());		
		System.out.println(set.contains("ufdhu"));
		System.out.println(set.contains("dfff"));	
		
	}
}

result ：

false
true
false