Java中的属性 getProperty(key, defaultValue) 方法及示例

Properties 类的getProperty(key, defaultValue)方法用于在此 Properties 对象中获取映射到此键的值，作为参数传递。此方法将获取此键的对应值（如果存在）并将其返回。如果没有这样的映射，则返回默认值。

句法：

public String getProperty(String key, String defaultValue)

编程需要懂一点英语

参数：此方法接受两个参数：

key ：要在此 Properties 对象中检查其映射。
defaultValue ：这是键的默认映射

返回：此方法返回与此键对应的提取值（如果存在）。如果没有这样的映射，则返回默认值。

下面的程序说明了 getProperty(key, defaultValue) 方法：

方案一：

// Java program to demonstrate
// getProperty(key, defaultValue) 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());
  
        // Getting the value of Pen
        System.out.println("Value of Pen: "
                           + properties
                                 .getProperty("Pen", 200));
  
        // Getting the value of Phone
        System.out.println("Value of Phone: "
                           + properties
                                 .getProperty("Phone", 200));
    }
}

输出：

Properties: {Book=500, Mobile=5000, Pen=10, Clothes=400}
Value of Pen: 10
Value of Phone: 200

方案二：

// Java program to demonstrate
// getProperty(key, defaultValue) 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());
  
        // Getting the value of 1
        System.out.println("Value of 1: "
                           + properties
                                 .getProperty(1, "200RS"));
  
        // Getting the value of 5
        System.out.println("Value of 5: "
                           + properties
                                 .getProperty(5, "200RS"));
    }
}

输出：

Current Properties: {3=1000RS, 2=500RS, 1=100RS}
Value of 1: 100RS
Value of 5: 200RS

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