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

用法:

public Object containsKey(Object value)

参数：此方法接受参数值，该参数值是要在此属性中搜索的键。

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

以下示例程序旨在说明containsKey(value)方法：

示例1:

// 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

示例2:

// 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：https://docs.oracle.com/javase/9​​/docs/api/java/util/Properties.html#containsKey-java.lang.Object-