Java中的属性 keySet() 方法及示例

Properties 类的keySet()方法用于从 Properties 中包含的关键元素中创建一个集合。它基本上返回键的集合视图，或者我们可以创建一个新集合并将键元素存储在其中。

句法：

public Set keySet()

参数：此方法不接受任何参数

返回：此方法返回此 Properties 对象中包含的键的Set 视图。

下面的程序显示了 int keySet() 方法的实现。

方案一：

// Java code to show the implementation of
// keySet() method
  
import java.util.*;
public class GfG {
  
    // Main method
    public static void main(String[] args)
    {
  
        // Create a properties and add some values
        Properties properties = new Properties();
        properties.put("Pen", 10);
        properties.put("Book", 500);
        properties.put("Clothes", 400);
        properties.put("Mobile", 5000);
  
        // Print Properties details
        System.out.println("Properties: "
                           + properties.toString());
  
        System.out.println("keySet: "
                           + properties.keySet());
    }
}

输出：

Properties: {Book=500, Mobile=5000, Pen=10, Clothes=400}
keySet: [Book, Mobile, Pen, Clothes]

方案二：

// Java program to demonstrate
// keySet() method.
  
import java.util.*;
  
public class GFG {
  
    // Main method
    public static void main(String[] args)
    {
  
        // Create a properties and add some values
        Properties properties = new Properties();
  
        // Inserting elements into the properties
        properties.put("Geeks", 10);
        properties.put("4", 15);
        properties.put("Geeks", 20);
        properties.put("Welcomes", 25);
        properties.put("You", 30);
  
        // Print Properties details
        System.out.println("Current Properties: "
                           + properties.toString());
  
        System.out.println("keySet: "
                           + properties.keySet());
    }
}

输出：

Current Properties: {You=30, Welcomes=25, 4=15, Geeks=20}
keySet: [You, Welcomes, 4, Geeks]

参考资料：https://docs.oracle.com/javase/9/docs/api/ Java/util/Properties.html#keySet–