Java中的属性 containsKey(value) 方法和示例

Properties 类的containsKey(value)方法用于检查此 Properties 对象是否包含此 Key 对其中存在的任何键的任何映射。它将这个值作为参数进行比较，并返回一个布尔值作为结果。

句法：

public Object containsKey(Object value)

参数：此方法接受一个参数值，该值是要在此属性中搜索的键。

返回：此方法返回一个布尔值，说明此键是否存在于此 Properties 对象中的结果。

下面的程序说明了 containsKey(value) 方法：

方案一：

// Java program to demonstrate
// containsKey(value) 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("Current Properties: "
                           + properties.toString());
  
        // Check if Pen is present or not
        // using containsKey()
        System.out.println("Is Pen present: "
                           + properties.containsKey("Pen"));
    }
}

输出：

Current Properties: {Book=500, Mobile=5000, Pen=10, Clothes=400}
Is Pen present: true

方案二：

// Java program to demonstrate
// containsKey(value) 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(1, "100RS");
        properties.put(2, "500RS");
        properties.put(3, "1000RS");
  
        // print Properties details
        System.out.println("Current Properties: "
                           + properties.toString());
  
        // Check if 5 is present or not
        // using containsKey()
        System.out.println("Is 5 present: "
                           + properties.containsKey(5));
    }
}

输出：

Current Properties: {3=1000RS, 2=500RS, 1=100RS}
Is 5 present: false

参考资料：https://docs.oracle.com/javase/9/docs/api/ Java/util/Properties.html#containsKey-java.lang.Object-