restful-java private vs public

Question

@XmlRootElement 
public class Activity { 
    private String description; 
    private int duration; 
    public String getDescription() { 
     return description; 
    } 
    public void setDescription(String description) { 
     this.description = description; 
    } 
    public int getDuration() { 
     return duration; 
    } 
    public void setDuration(int duration) { 
     this.duration = duration; 
    } 

這是代碼正常工作。但是，當改變第三和第四線公共

public String description; 
public int duration; 

我得到錯誤500.我不明白什麼是錯的public成員類型。每個對象都可以訪問public成員類型。請同時解釋何時使用public或private？

Answer 1

錯誤500不是真正的錯誤。看看你的日誌，你很可能會看到真正的錯誤。

這裏是一個MCVE（最小的，完整的和可驗證的例子）：

import javax.xml.bind.JAXBContext; 
import javax.xml.bind.annotation.XmlRootElement; 

public class Test { 
    public static void main(String[] args) throws Exception { 
     JAXBContext.newInstance(Activity.class); 
    } 
} 
@XmlRootElement 
class Activity { 
    public String description; 
    public int duration; 
    public String getDescription() { 
     return description; 
    } 
    public void setDescription(String description) { 
     this.description = description; 
    } 
    public int getDuration() { 
     return duration; 
    } 
    public void setDuration(int duration) { 
     this.duration = duration; 
    } 
} 

運行它給這個錯誤：

Exception in thread "main" com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 2 counts of IllegalAnnotationExceptions 
Class has two properties of the same name "description" 
    this problem is related to the following location: 
     at public java.lang.String Activity.getDescription() 
     at Activity 
    this problem is related to the following location: 
     at public java.lang.String Activity.description 
     at Activity 
Class has two properties of the same name "duration" 
    this problem is related to the following location: 
     at public int Activity.getDuration() 
     at Activity 
    this problem is related to the following location: 
     at public int Activity.duration 
     at Activity 

    at com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException$Builder.check(IllegalAnnotationsException.java:91) 
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:445) 
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:277) 
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:124) 
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1123) 
    at com.sun.xml.internal.bind.v2.ContextFactory.createContext(ContextFactory.java:147) 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
    at java.lang.reflect.Method.invoke(Method.java:498) 
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:247) 
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:234) 
    at javax.xml.bind.ContextFinder.find(ContextFinder.java:462) 
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:641) 
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584) 
    at Test.main(Test.java:7) 

正如你看到的，讓現場public意味着JAXB看到兩個同名的屬性，一個由public字段定義，另一個由Bean方法定義。

由於如果將字段public設置爲getter和setter方法沒有任何意義，如果您希望字段爲public，請刪除方法。我建議不要讓他們public。你爲什麼？當你有getter和setter方法來訪問字段時，並不需要。