In Java, there are many ways to traverse HashMap. Here are several common traversal methods to you.
1. Use keySet() to traverse the key, and then get the value through the key
- Create a HashMap object and add some key-value pairs to it.
- Use the () method to get a collection of all keys in a HashMap.
- Loop through this key collection via for-each.
- In the loop body, use the (key) method to obtain the corresponding value based on the current key and print out the key and value.
package ;
import ;
import ;
public class Test03 {
public static void main(String[] args) {
// Create a HashMap and add elements Map<String, String> map = new HashMap<>();
("Zhang Fei", "male");
("Sun Shangxiang", "female");
("Guan Yu", "male");
("Diao Chan", "female");
// traversal key collection for (String key : ()) {
// Get the value according to the key String value = (key);
("Key: " + key + ", Value: " + value);
}
}
}
2. Use entrySet() to traverse key-value pairs
- First create a HashMap object and add a key-value pair.
- Use the () method to get a collection containing all key-value pairs.
- Iterate through this collection through the for-each loop, and each loop gets an object.
- In the loop body, use the () method to get the keys, use the () method to get the values, and print them out.
package ;
import ;
import ;
public class Test03 {
public static void main(String[] args) {
// Create a HashMap and add elements Map<String, String> map = new HashMap<>();
("Zhang Fei", "male");
("Sun Shangxiang", "female");
("Guan Yu", "male");
("Diao Chan", "female");
// traverse key-value pair collection for (<String, String> entry : ()) {
// Get key String key = ();
// Get the value String value = ();
("Key: " + key + ", Value: " + value);
}
}
}
3. Use the forEach() method (Java 8 and above)
- Create a HashMap and add elements.
- Call the () method and pass a Lambda expression. Parameters key and value of Lambda expressions
Represents the keys and values currently traversed. - In the method body of a Lambda expression, print the keys and values.
package ;
import ;
import ;
public class Test03 {
public static void main(String[] args) {
// Create a HashMap and add elements Map<String, String> map = new HashMap<>();
("Zhang Fei", "male");
("Sun Shangxiang", "female");
("Guan Yu", "male");
("Diao Chan", "female");
// Use the forEach method to traverse ((key, value) -> {
("Key: " + key + ", Value: " + value);
});
}
}
4. Use iterator to traverse
- Create a HashMap and add elements.
- Use the ().iterator() method to get the iterator of the set of key-value pairs.
- Use the while loop combination () method to determine whether there is another element.
- In the loop body, use the () method to get the next object, then get the keys and values and print the output.
package ;
import ;
import ;
import ;
public class Test03 {
public static void main(String[] args) {
// Create a HashMap and add elements Map<String, String> map = new HashMap<>();
("Zhang Fei", "male");
("Sun Shangxiang", "female");
("Guan Yu", "male");
("Diao Chan", "female");
// Get the iterator for the set of key-value pairs Iterator<<String, String>> iterator = ().iterator();
// Use iterator to traverse while (()) {
<String, String> entry = ();
String key = ();
String value = ();
("Key: " + key + ", Value: " + value);
}
}
}
5. Iterate through all keys
Note that it is just traversing the key value, that is, the key value, the code is as follows:
package ;
import ;
import ;
public class Test03 {
public static void main(String[] args) {
// Create a HashMap and add elements Map<String, String> map = new HashMap<>();
("Zhang Fei", "male");
("Sun Shangxiang", "female");
("Guan Yu", "male");
("Diao Chan", "female");
// Iterate through all keys for (String key : ()) {
("key : " + key);
}
}
}
6. Iterate through all values
Note that it is just traversing the value of the key-value pair, that is, the code is as follows:
package ;
import ;
import ;
public class Test03 {
public static void main(String[] args) {
// Create a HashMap and add elements Map<String, String> map = new HashMap<>();
("Zhang Fei", "male");
("Sun Shangxiang", "female");
("Guan Yu", "male");
("Diao Chan", "female");
// Iterate through all keys for (String key : ()) {
("value： " + key);
}
}
}Summarize
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