The "unchecked or unsafe operations" warning was added when java added Generics, if I remember correctly. It's usually asking you to be more explicit about types, in one way or another.
For example. the code ArrayList foo = new ArrayList(); triggers that warning because javac is looking for ArrayList<String> foo = new ArrayList<String>();
for example when you call a function that returns Generic Collections and you don't specify the generic parameters yourself.
for a function
List<String> getNames()
List names = obj.getNames();
will generate this error.
To solve it you would just add the parameters
List<String> names = obj.getNames();
The solution would be to use specific type in <> like ArrayList<File>.
example:
File curfolder = new File( "C:\\Users\\username\\Desktop");
File[] file = curfolder.listFiles();
ArrayList filename = Arrays.asList(file);
above code generate warning because ArrayList is not of specific type.
File curfolder = new File( "C:\\Users\\username\\Desktop");
File[] file = curfolder.listFiles();
ArrayList<File> filename = Arrays.asList(file);
above code will do fine. Only change is in third line after ArrayList.
The "unchecked or unsafe operations" warning was added when java added Generics, if I remember correctly. It's usually asking you to be more explicit about types, in one way or another.
For example. the code ArrayList foo = new ArrayList(); triggers that warning because javac is looking for ArrayList<String> foo = new ArrayList<String>();
for example when you call a function that returns Generic Collections and you don't specify the generic parameters yourself.
for a function
List<String> getNames()
List names = obj.getNames();
will generate this error.
To solve it you would just add the parameters
List<String> names = obj.getNames();
I just want to add one example of the kind of unchecked warning I see quite often. If you use classes that implement an interface like Serializable, often you will call methods that return objects of the interface, and not the actual class. If the class being returned must be cast to a type based on generics, you can get this warning.
Here is a brief (and somewhat silly) example to demonstrate:
import java.io.Serializable;
public class SimpleGenericClass<T> implements Serializable {
public Serializable getInstance() {
return this;
}
// @SuppressWarnings("unchecked")
public static void main() {
SimpleGenericClass<String> original = new SimpleGenericClass<String>();
// java: unchecked cast
// required: SimpleGenericClass<java.lang.String>
// found: java.io.Serializable
SimpleGenericClass<String> returned =
(SimpleGenericClass<String>) original.getInstance();
}
}
getInstance() returns an object that implements Serializable. This must be cast to the actual type, but this is an unchecked cast.
If you do what it suggests and recompile with the "-Xlint:unchecked" switch, it will give you more detailed information.
As well as the use of raw types (as described by the other answers), an unchecked cast can also cause the warning.
Once you've compiled with -Xlint, you should be able to rework your code to avoid the warning. This is not always possible, particularly if you are integrating with legacy code that cannot be changed. In this situation, you may decide to suppress the warning in places where you know that the code is correct:
@SuppressWarnings("unchecked")
public void myMethod()
{
//...
}
The solution would be to use specific type in <> like ArrayList<File>.
example:
File curfolder = new File( "C:\\Users\\username\\Desktop");
File[] file = curfolder.listFiles();
ArrayList filename = Arrays.asList(file);
above code generate warning because ArrayList is not of specific type.
File curfolder = new File( "C:\\Users\\username\\Desktop");
File[] file = curfolder.listFiles();
ArrayList<File> filename = Arrays.asList(file);
above code will do fine. Only change is in third line after ArrayList.
I had 2 years old classes and some new classes. I solved it in Android Studio as follows:
allprojects {
gradle.projectsEvaluated {
tasks.withType(JavaCompile) {
options.compilerArgs << "-Xlint:unchecked"
}
}
}
In my project build.gradle file (Borzh solution)
And then if some Metheds is left:
@SuppressWarnings("unchecked")
public void myMethod()
{
//...
}
The "unchecked or unsafe operations" warning was added when java added Generics, if I remember correctly. It's usually asking you to be more explicit about types, in one way or another.
For example. the code ArrayList foo = new ArrayList(); triggers that warning because javac is looking for ArrayList<String> foo = new ArrayList<String>();
for example when you call a function that returns Generic Collections and you don't specify the generic parameters yourself.
for a function
List<String> getNames()
List names = obj.getNames();
will generate this error.
To solve it you would just add the parameters
List<String> names = obj.getNames();
If you do what it suggests and recompile with the "-Xlint:unchecked" switch, it will give you more detailed information.
As well as the use of raw types (as described by the other answers), an unchecked cast can also cause the warning.
Once you've compiled with -Xlint, you should be able to rework your code to avoid the warning. This is not always possible, particularly if you are integrating with legacy code that cannot be changed. In this situation, you may decide to suppress the warning in places where you know that the code is correct:
@SuppressWarnings("unchecked")
public void myMethod()
{
//...
}
For Android Studio, you need to add:
allprojects {
gradle.projectsEvaluated {
tasks.withType(JavaCompile) {
options.compilerArgs << "-Xlint:unchecked"
}
}
// ...
}
in your project's build.gradle file to know where this error is produced.
This warning means that your code operates on a raw type, recompile the example with the
-Xlint:unchecked
to get the details
like this:
javac YourFile.java -Xlint:unchecked
Main.java:7: warning: [unchecked] unchecked cast
clone.mylist = (ArrayList<String>)this.mylist.clone();
^
required: ArrayList<String>
found: Object
1 warning
docs.oracle.com talks about it here: http://docs.oracle.com/javase/tutorial/java/generics/rawTypes.html
for example when you call a function that returns Generic Collections and you don't specify the generic parameters yourself.
for a function
List<String> getNames()
List names = obj.getNames();
will generate this error.
To solve it you would just add the parameters
List<String> names = obj.getNames();
If you do what it suggests and recompile with the "-Xlint:unchecked" switch, it will give you more detailed information.
As well as the use of raw types (as described by the other answers), an unchecked cast can also cause the warning.
Once you've compiled with -Xlint, you should be able to rework your code to avoid the warning. This is not always possible, particularly if you are integrating with legacy code that cannot be changed. In this situation, you may decide to suppress the warning in places where you know that the code is correct:
@SuppressWarnings("unchecked")
public void myMethod()
{
//...
}
This warning also could be raised due to
new HashMap() or new ArrayList() that is generic type has to be specific otherwise the compiler will generate warning.
Please make sure that if you code contains the following you have to change accordingly
new HashMap() => Map map = new HashMap() new HashMap() => Map map = new HashMap<>()
new ArrayList() => List map = new ArrayList() new ArrayList() => List map = new ArrayList<>()
I have ArrayList<Map<String, Object>> items = (ArrayList<Map<String, Object>>) value;. Because value is a complex structure (I want to clean JSON), there can happen any combinations on numbers, booleans, strings, arrays. So, I used the solution of @Dan Dyer:
@SuppressWarnings("unchecked")
ArrayList<Map<String, Object>> items = (ArrayList<Map<String, Object>>) value;
For Android Studio, you need to add:
allprojects {
gradle.projectsEvaluated {
tasks.withType(JavaCompile) {
options.compilerArgs << "-Xlint:unchecked"
}
}
// ...
}
in your project's build.gradle file to know where this error is produced.
You can keep it in the generic form and write it as:
// list 2 is made generic and can store any type of Object
ArrayList<Object> list2 = new ArrayList<Object>();
Setting type of ArrayList as Object gives us the advantage to store any type of data. You don't need to use -Xlint or anything else.
I have ArrayList<Map<String, Object>> items = (ArrayList<Map<String, Object>>) value;. Because value is a complex structure (I want to clean JSON), there can happen any combinations on numbers, booleans, strings, arrays. So, I used the solution of @Dan Dyer:
@SuppressWarnings("unchecked")
ArrayList<Map<String, Object>> items = (ArrayList<Map<String, Object>>) value;
This warning also could be raised due to
new HashMap() or new ArrayList() that is generic type has to be specific otherwise the compiler will generate warning.
Please make sure that if you code contains the following you have to change accordingly
new HashMap() => Map map = new HashMap() new HashMap() => Map map = new HashMap<>()
new ArrayList() => List map = new ArrayList() new ArrayList() => List map = new ArrayList<>()
This warning means that your code operates on a raw type, recompile the example with the
-Xlint:unchecked
to get the details
like this:
javac YourFile.java -Xlint:unchecked
Main.java:7: warning: [unchecked] unchecked cast
clone.mylist = (ArrayList<String>)this.mylist.clone();
^
required: ArrayList<String>
found: Object
1 warning
docs.oracle.com talks about it here: http://docs.oracle.com/javase/tutorial/java/generics/rawTypes.html
I just want to add one example of the kind of unchecked warning I see quite often. If you use classes that implement an interface like Serializable, often you will call methods that return objects of the interface, and not the actual class. If the class being returned must be cast to a type based on generics, you can get this warning.
Here is a brief (and somewhat silly) example to demonstrate:
import java.io.Serializable;
public class SimpleGenericClass<T> implements Serializable {
public Serializable getInstance() {
return this;
}
// @SuppressWarnings("unchecked")
public static void main() {
SimpleGenericClass<String> original = new SimpleGenericClass<String>();
// java: unchecked cast
// required: SimpleGenericClass<java.lang.String>
// found: java.io.Serializable
SimpleGenericClass<String> returned =
(SimpleGenericClass<String>) original.getInstance();
}
}
getInstance() returns an object that implements Serializable. This must be cast to the actual type, but this is an unchecked cast.
The "unchecked or unsafe operations" warning was added when java added Generics, if I remember correctly. It's usually asking you to be more explicit about types, in one way or another.
For example. the code ArrayList foo = new ArrayList(); triggers that warning because javac is looking for ArrayList<String> foo = new ArrayList<String>();
I had 2 years old classes and some new classes. I solved it in Android Studio as follows:
allprojects {
gradle.projectsEvaluated {
tasks.withType(JavaCompile) {
options.compilerArgs << "-Xlint:unchecked"
}
}
}
In my project build.gradle file (Borzh solution)
And then if some Metheds is left:
@SuppressWarnings("unchecked")
public void myMethod()
{
//...
}
You can keep it in the generic form and write it as:
// list 2 is made generic and can store any type of Object
ArrayList<Object> list2 = new ArrayList<Object>();
Setting type of ArrayList as Object gives us the advantage to store any type of data. You don't need to use -Xlint or anything else.
If you do what it suggests and recompile with the "-Xlint:unchecked" switch, it will give you more detailed information.
As well as the use of raw types (as described by the other answers), an unchecked cast can also cause the warning.
Once you've compiled with -Xlint, you should be able to rework your code to avoid the warning. This is not always possible, particularly if you are integrating with legacy code that cannot be changed. In this situation, you may decide to suppress the warning in places where you know that the code is correct:
@SuppressWarnings("unchecked")
public void myMethod()
{
//...
}
Source: Stackoverflow.com