java中常见错误

编译器错误

编译器错误信息是在Java软件代码通过编译器运行时创建的.一定要记住,编译器可能会为一个错误抛出许多错误信息.因此,修复第一个错误并重新编译,可以解决很多问题。

1. “… expected”

缺少分号";"或右括号")"

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

2. “unclosed string literal”

字符串不以引号结束

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”

产生原因很多,错误信息帮助不大

} // 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”

• 标识符在声明时的拼写可能与在代码中使用时不同
• 变量未被声明
• 变量在声明的范围之外使用
• 没有导入类

5. “public class XXX should be in file”

类名和文件名不匹配

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”

类型不一致

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

7. “invalid method declaration; return type required”

没有声明返回类型

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”

入参类型错误

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”

没有写返回语句

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”

精度丢失,如

• 将实数赋值给 int 类型的变量
• 将 double 类型数据赋值给 int 类型的变量

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”

存在语句执行不到

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

13. “variable might not have been initialized”

变量未初始化

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

14. “Operator .. cannot be applied to ”

使用了未定义的类型

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

15. “inconvertible types”

类型无法强转,如: 布尔值无法转为整型

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

16. “missing return value”

没有出参或出参类型不正确

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

返回值类型为 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”

静态方法引用非静态变量

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”

声明了数组,但没有初始化

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

参考