java中常見錯誤

編譯器錯誤

編譯器錯誤信息是在Java軟件代碼通過編譯器運行時創建的.一定要記住,編譯器可能會為一個錯誤拋出許多錯誤信息.因此,修復第一個錯誤並重新編譯,可以解決很多問題。

1. “… expected”

缺少分號";"或右括號")"

private static double volume(String solidom, double alturam, double areaBasem, double raiom) {
	double vol;
	if (solidom.equalsIgnoreCase("esfera"){
		vol=(4.0/3)*Math.pi*Math.pow(raiom,3);
	}
	else {
		if (solidom.equalsIgnoreCase("cilindro") {
			vol=Math.pi*Math.pow(raiom,2)*alturam;
		}else {
			vol=(1.0/3)*Math.pi*Math.pow(raiom,2)*alturam;
		}
	}
	return vol;
}

2. “unclosed string literal”

字符串不以引號結束

public abstract class NFLPlayersReference {
	private static Runningback[] nflplayersreference;
	private static Quarterback[] players;
	private static WideReceiver[] nflplayers;
	public static void main(String args[]){
	Runningback r = new Runningback("Thomlinsion");
	Quarterback q = new Quarterback("Tom Brady");
	WideReceiver w = new WideReceiver("Steve Smith");
	NFLPlayersReference[] NFLPlayersReference;
		Run();// {
		NFLPlayersReference = new NFLPlayersReference [3];
		nflplayersreference[0] = r;
		players[1] = q;
		nflplayers[2] = w;
			for ( int i = 0; i < nflplayersreference.length; i++ ) {
			System.out.println("My name is " + " nflplayersreference[i].getName());
			nflplayersreference[i].run();
			nflplayersreference[i].run();
			nflplayersreference[i].run();
			System.out.println("NFL offensive threats have great running abilities!");
		}
	}
	private static void Run() {
		System.out.println("Not yet implemented");
	}
}

3. “illegal start of an expression”

產生原因很多,錯誤信息幫助不大

} // ADD IT HERE
   public void newShape(String shape) {
    switch (shape) {
        case "Line":
            Shape line = new Line(startX, startY, endX, endY);
        shapes.add(line);
        break;
            case "Oval":
        Shape oval = new Oval(startX, startY, endX, endY);
        shapes.add(oval);
        break;
        case "Rectangle":
        Shape rectangle = new Rectangle(startX, startY, endX, endY);
        shapes.add(rectangle);
        break;
        default:
        System.out.println("ERROR. Check logic.");
    }
    }
} // REMOVE IT FROM HERE
}

4. “cannot find symbol”

• 標識符在聲明時的拼寫可能與在代碼中使用時不同
• 變量未被聲明
• 變量在聲明的范圍之外使用
• 沒有導入類

5. “public class XXX should be in file”

類名和文件名不匹配

package javaapplication3;
  public class Robot {
    int xlocation;
    int ylocation;
    String name;
    static int ccount = 0;
    public Robot(int xxlocation, int yylocation, String nname) {
        xlocation = xxlocation;
        ylocation = yylocation;
        name = nname;
        ccount++;
    }
}

  public class JavaApplication1 {
	public static void main(String[] args) {
    	robot firstRobot = new Robot(34,51,"yossi");
    	System.out.println("numebr of robots is now " + Robot.ccount);
	}
}

6. “incompatible types”

類型不一致

test.java:78: error: incompatible types
return stringBuilder.toString();
required: int
found: String
1 error

7. “invalid method declaration; return type required”

沒有聲明返回類型

public class Circle
{
	private double radius;
	public CircleR(double r)
	{
    	radius = r;
	}
	 public diameter()
	{
    double d = radius * 2;
    return d;
	}
}

8. “method in class cannot be applied to given types”

入參類型錯誤

RandomNumbers.java:9: error: method generateNumbers in class RandomNumbers cannot be applied to given types;
generateNumbers();
required: int[]
found:generateNumbers();
reason: actual and formal argument lists differ in length

9. “missing return statement”

沒有寫返回語句

public String[] OpenFile() throws IOException {
	Map<String, Double> map = new HashMap();
	FileReader fr = new FileReader("money.txt");
	BufferedReader br = new BufferedReader(fr);
	try{
    	while (br.ready()){
        	String str = br.readLine();
        	String[] list = str.split(" ");
        	System.out.println(list);
    	}
	}catch (IOException e){
    	System.err.println("Error - IOException!");
	 }
}

10. “possible loss of precision”

精度丟失,如

• 將實數賦值給 int 類型的變量
• 將 double 類型數據賦值給 int 類型的變量

11. “reached end of file while parsing”

缺少"}"

public class mod_MyMod extends BaseMod
	public String Version()
	{
		return "1.2_02";
	}
	public void AddRecipes(CraftingManager recipes)
	{
		recipes.addRecipe(new ItemStack(Item.diamond), new Object[] {
			"#", Character.valueOf('#'), Block.dirt
		});
	}

12. “unreachable statement”

存在語句執行不到

for(;;){
	break;
... // unreachable statement
}
int i=1;
if(i==1)
	...
else
	... // dead code

13. “variable might not have been initialized”

變量未初始化

int x;
if (condition) {
	x = 5;
}
System.out.println(x); // x may not have been initialized

14. “Operator .. cannot be applied to ”

使用了未定義的類型

operator < cannot be applied to java.lang.Object,java.lang.Object

15. “inconvertible types”

類型無法強轉,如: 布爾值無法轉為整型

TypeInvocationConversionTest.java:12: inconvertible types found : java.util.ArrayList<java.lang.Class<? extends TypeInvocationConversionTest.Interface1>>
required: java.util.ArrayList<java.lang.Class<?>>
lessRestrictiveClassList = (ArrayList<Class<?>>) classList;

16. “missing return value”

沒有出參或出參類型不正確

17. “cannot return a value from method whose result type is void”

返回值類型為 void,但是有返回值

public static void move()
{
	System.out.println("What do you want to do?");
	Scanner scan = new Scanner(System.in);
	int userMove = scan.nextInt();
	return userMove;
}

18. “non-static variable . . . cannot be referenced from a static context”

靜態方法引用非靜態變量

public class StaticTest {
private int count=0;
	public static void main(String args[]) throws IOException {
		count++; //compiler error: non-static variable count cannot be referenced from a static context
	}
}

19. “non-static method . . . cannot be referenced from a static context”

class Sample
{
	private int age;
	public void setAge(int a)
	{
   		age=a;
	}
	public int getAge()
	{
   		return age;
	}
	public static void main(String args[])
	{
		System.out.println(“Age is:”+ getAge());
	}
}

20. “(array) not initialized”

聲明了數組,但沒有初始化

AClass[] array = {object1, object2}
   As is:
   AClass[] array = new AClass[2];
   …
   array[0] = object1;
   array[1] = object2;
   But not:
   AClass[] array;
   …
   array = {object1, object2};

參考