Map interface

Relationship

Common methods

1.put(K key, V value)

effect ：

Will key （key）/ value （value） Map to Map Collection , Simply put, it is equivalent to the two values you enter key and values Each is a circle , Then they are surrounded by a big circle , When you call , If no other method to separate them is called , Generally, they call the big circle formed by them directly .

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
    
	public static void main(String[] args) {
    
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);		
		System.out.println(hashmap.get("key"));
	}
}

result ：

35663

2.get(Object key)

effect ：

Returns the specified key key Mapped values , There is no the key The corresponding value returns null.

notes ： Can only be key .

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
	public static void main(String[] args) {
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);	
		hashmap.put("srht", 32757);
		hashmap.put("ht", 3465);
		System.out.println(hashmap.get("key"));
	}
}

result ：

35663

3.size()

effect ：

return Map The amount of data in the collection

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
	public static void main(String[] args) {
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);	
		hashmap.put("srht", 32757);
		hashmap.put("ht", 3465);		
		System.out.println(hashmap.size());
	}
}

result ：

3

4.clear()

effect ：

Empty Map aggregate

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
	public static void main(String[] args) {
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);	
		hashmap.put("srht", 32757);
		hashmap.put("ht", 3465);		
		System.out.println(hashmap.size());
		hashmap.clear();
		System.out.println(hashmap.size());
	}
}

result ：

3
0

5.isEmpty ()

effect ：

Judge Map Whether there is data in the collection , If not, return true, Otherwise return to false

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
	public static void main(String[] args) {
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);	
		hashmap.put("srht", 32757);
		hashmap.put("ht", 3465);		
		System.out.println(hashmap.isEmpty());
		
		hashmap.clear();
		System.out.println(hashmap.isEmpty());
	}
}

result ：

false
true

6.remove(Object key)

effect ：

Delete Map Collect the data of the key in the and return its corresponding value value .

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
	public static void main(String[] args) {
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);	
		hashmap.put("srht", 32757);
		hashmap.put("ht", 3465);			
		System.out.println(hashmap.remove("key"));
		System.out.println(hashmap.size());		
	}
}

result ：

35663
2

7.values()

effect ：

return Map All in the assembly value Consisting of Collection Data type format data .

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
	public static void main(String[] args) {
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);	
		hashmap.put("srht", 32757);
		hashmap.put("ht", 3465);			
		System.out.println(hashmap.remove("key"));
		System.out.println(hashmap.values());
		System.out.println(hashmap.size());		
	}
}

result ：

35663
[3465, 32757]
2

8.contains Key(Object key)

effect ：

Determine whether the specified key is included in the set , Include return true, Otherwise return to false

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
	public static void main(String[] args) {
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);	
		hashmap.put("srht", 32757);
		hashmap.put("ht", 3465);			
		System.out.println(hashmap.remove("key"));
		System.out.println(hashmap.values());
		System.out.println(hashmap.size());		
		System.out.println(hashmap.containsKey("dfshl"));
	}
}

result ：

35663
[3465, 32757]
2
false

9.containsValue(Object value)

effect ：

Determine whether the set contains the specified value , Include return true, Otherwise return to false

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
	public static void main(String[] args) {
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);	
		hashmap.put("srht", 32757);
		hashmap.put("ht", 3465);			
		System.out.println(hashmap.remove("key"));
		System.out.println(hashmap.values());
		System.out.println(hashmap.size());		
		System.out.println(hashmap.containsKey("dfshl"));
		System.out.println(hashmap.containsValue(3465));
	}
}

result ：

35663
[3465, 32757]
2
false
true

10.keySet()

effect ：

return Map All in the assembly key Composed of Set aggregate

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
	public static void main(String[] args) {
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);	
		hashmap.put("srht", 32757);
		hashmap.put("ht", 3465);			
		System.out.println(hashmap.remove("key"));
		System.out.println(hashmap.values());
		System.out.println(hashmap.size());		
		System.out.println(hashmap.containsKey("dfshl"));
		System.out.println(hashmap.containsValue(3465));
		System.out.println(hashmap.keySet());
	}
}

result ：

35663
[3465, 32757]
2
false
true
[ht, srht]

11.entrySet()

effect ：

take Map Assemble each key-value Convert to a Entry Object and return by all Entry Made up of objects Set aggregate

example ：

package Hashmap;

import java.util.HashMap;

public class Test {
	public static void main(String[] args) {
		HashMap<String,Integer> hashmap=new HashMap<>();
		hashmap.put("key", 35663);	
		hashmap.put("srht", 32757);
		hashmap.put("ht", 3465);			
		System.out.println(hashmap.entrySet());
	}
}

result ：

[ht=3465, key=35663, srht=32757]