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Java开关语句:需要常量表达式,但它是常数

compile-time-constant java

143

Austin Hyde · 技术社区 · 15 年前

所以,我正在处理这个类,它有一些静态常量:

public abstract class Foo {
    ...
    public static final int BAR;
    public static final int BAZ;
    public static final int BAM;
    ...
}

然后,我想要一种基于常量得到相关字符串的方法:

public static String lookup(int constant) {
    switch (constant) {
        case Foo.BAR: return "bar";
        case Foo.BAZ: return "baz";
        case Foo.BAM: return "bam";
        default: return "unknown";
    }
}

但是,当我编译时,我得到一个 constant expression required 3个案例标签中的每一个都有错误。

我知道编译器需要在编译时知道表达式才能编译开关,但为什么不呢? Foo.BA_ 常数?

10 回复 | 直到 7 年前

131

Stephen C 7 年前

Â§15.28 Constant Expressions Â§4.12.4 Final Variables

final

enum int switch default case Why is default required for a switch on an enum in this code?

Tony Ennis 15 年前

public abstract class Foo {
    ...
    public static final int BAR=0;
    public static final int BAZ=1;
    public static final int BAM=2;
    ...
}

Teo Inke 11 年前

public static final int TAKE_PICTURE = 1;

public static int TAKE_PICTURE = 1;

Sheldon L. Cooper 15 年前

public static final int BAR = new Random().nextInt();

BAR

Cosmin 14 年前

public class MainClass {
enum Choice { Choice1, Choice2, Choice3 }
public static void main(String[] args) {
Choice ch = Choice.Choice1;

switch(ch) {
  case Choice1:
    System.out.println("Choice1 selected");
    break;
 case Choice2:
   System.out.println("Choice2 selected");
   break;
 case Choice3:
   System.out.println("Choice3 selected");
   break;
    }
  }
}

Switch statement with enum

Mahdi-Malv 8 年前

switch(view.getTag()) {//which is an Object type

   case 0://will give compiler error that says Constant expression required

   //...
}

switch((int)view.getTag()) {//will be int

   case 0: //No Error

   //...
}

Ojonugwa Jude Ochalifu Dave 7 年前

 roleSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

            switch (parent.getItemAtPosition(position)) {
                case ADMIN_CONSTANT: //Threw the error

            }

public static final String ADMIN_CONSTANT= "Admin";

roleSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

            String selectedItem = String.valueOf(parent.getItemAtPosition(position));
            switch (selectedItem) {
                case ADMIN_CONSTANT:

            }

Janaco 7 年前

switch (tipoWebServ) {
                            case VariablesKmDialog.OBTENER_KM:
                                resultObtenerKm(result);
                                break;
                            case var.MODIFICAR_KM:
                                resultModificarKm(result);
                                break;
                        }

var.MODIFICAR_KM: VariablesKmDialog.OBTENER_KM

Samer Murad 7 年前

if switch

-1

everton Raghunandan Krishnamurthy 14 年前

public enum Foo 
{
    BAR("bar"),
    BAZ("baz"),
    BAM("bam");

    private final String description;

    private Foo(String description)
    {
        this.description = description;
    }

    public String getDescription()
    {
        return description;
    }
}

System.out.println(Foo.BAR.getDescription());