Java:通过键从 Hashmap 获取对象

Question

我尝试刷新我的 Java 技能。但现在我陷入了 HashMap 。我没有拿回正确的对象。这是我的示例代码:

public class Sample {

    private static Map<String, Map<String, String>> peaks = new HashMap<String, Map<String, String>>();
    private final String name;

    public Sample(String name) {
        this.name = name;
        this.peaks = new HashMap<String, Map<String, String>>();
    }

    public static Map<String, Map<String, String>> getPeaks() {
        return peaks;}

    public static void addPeak(String peakName, String value) {
        Map<String, String> peak = new HashMap<String, String>();
        peak.put("value", value);
        peaks.put(peakName, peak);
    }
}

public class Main {
    static Map<Integer, Sample> sample = new HashMap<Integer, Sample>();

    public static void main(String[] args) {
        Sample sam = new Sample("Test1");
        sample.put(1, sam);
        sample.get(1).addPeak("A", "1");

        sam = new Sample("Test2");
        sample.put(2, sam);
        sample.get(2).addPeak("B", "123");

        System.out.println(sample.get(1).getPeaks().toString());    
        System.out.println(sample.get(2).getPeaks().toString());    
        System.out.println(sample.get(4).getPeaks().toString());    
    }
}

每次输出都是:{B={value=123}}

我不知道哪个部分是错误的。我错过了什么吗？

Answer 1

此 map 是静态的:

private static Map<String, Map<String, String>> peaks = new HashMap<String, Map<String, String>>();

因此，每次调用 Sample.getPeaks() 都指向同一个 Map。

//getPeaks() returns the same map in both cases.
// In other words : sample.get(1).getPeaks() == sample.get(2).getPeaks()
System.out.println(sample.get(1).getPeaks().toString());    
System.out.println(sample.get(2).getPeaks().toString());

// This is equivalent to
Map<String, Map<String, String>> myStaticMap = Sample.getPeaks();
System.out.println(myStaticMap.toString());    
System.out.println(myStaticMap.toString());