Question

我想创建一个常量ArrayList，但我保持返回空结果。

请注释这是声明静态最终数组列表的正确方法吗？

public final class Constants {
    public static ArrayList<String[]> points = new ArrayList<String[]>();
    {
        points.add( new String[] {"A","5.42420782","100.2680779" } );
        points.add( new String[] {"B","5.42253496","100.26634007" } );
        points.add( new String[] {"C","5.4196543","100.2645124" } );
        points.add( new String[] {"D", "5.41808928","100.26244618" } );
    }

    public static final List<ArrayList<String[]>> fix_points = Collections.unmodifiableList(Arrays.asList(points));
}

尝试以循环方式返回。

for(ArrayList<String[]> item : Constants.fix_points) {
   System.out.println(item);
}

打印显示空[]。

Answer 1

您需要了解启动块和静态块之间的区别。

{
        points.add( new String[] {"A","5.42420782","100.2680779" } );
        points.add( new String[] {"B","5.42253496","100.26634007" } );
        points.add( new String[] {"C","5.4196543","100.2645124" } );
        points.add( new String[] {"D", "5.41808928","100.26244618" } );
    }

在创建常量实例时调用。

哪里

static {
        points.add( new String[] {"A","5.42420782","100.2680779" } );
        points.add( new String[] {"B","5.42253496","100.26634007" } );
        points.add( new String[] {"C","5.4196543","100.2645124" } );
        points.add( new String[] {"D", "5.41808928","100.26244618" } );
    }

在类加载时调用。

您需要后一个块，即静态块。

Answer 2

替换下面的行

List<ArrayList<String[]>> fix_points = Collections.unmodifiableList(Arrays.asList(points));

final List<String[]> fix_points = Collections.unmodifiableList(points);

 final List<String[]> fix_points = Collections.unmodifiableList(points);
    for(String[] item : fix_points) {
        for(int i=0;i<item.length;i++)
            System.out.println(item[i]);
}

Answer 3

我不知道为什么你需要一个List<ArrayList<String[]>>，但产生的输出应该是（String[].toString()）

[[Ljava.lang.String;@29ce4d9c, [Ljava.lang.String;@b24c3a5, [Ljava.lang.String;@28e1c37a, [Ljava.lang.String;@1c0b972b]

您可以使用

打印确切的内容

for(ArrayList<String[]> item : Constants.fix_points) {
     for (String[] i : item) {
        Log.d(getClass().getSimpleName(), " " + i[0]+ " " +  i [1]);
     }
}

创建常量Arraylist返回空

3 个答案: