Java : @SuppressWarnings (annotation) with Examples

October 18, 2023

日本語

SuppressWarnings (Java SE 20 & JDK 20) with Examples.
You will find code examples on most SuppressWarnings methods.

Summary

Four kinds of warnings that can be specified by @SuppressWarnings:

• unchecked
• deprecation
• removal
• preview

Please see also Java Language Specification :

• 9.6.4.5. @SuppressWarnings (Java SE 20)

An example of a warning :

public class Foo {
    // This code intentionally omit the type parameter E for List<E>.
    public void m(List list) {
        list.add("aaa");
    }
}

//> javac -Xlint:unchecked Foo.java
//Foo.java:8: warning: [unchecked] unchecked call to add(E) as a member of the raw type List
//        list.add("aaa");
//                ^
//  where E is a type-variable:
//    E extends Object declared in interface List
//1 warning

An example of suppressing warnings :

public class Bar {
    @SuppressWarnings("unchecked")
    public void m(List list) {
        list.add("aaa");
    }
}

//> javac -Xlint:unchecked Bar.java
// <No errors and warnings>

An example of a warning :

@Deprecated
public class Sample {
}

public class Foo {
    public void m() {
        final var sample = new Sample();
        System.out.println(sample);
    }
}

//> javac -Xlint:deprecation Foo.java
//Foo.java:5: warning: [deprecation] Sample in unnamed package has been deprecated
//        final var sample = new Sample();
//                               ^
//1 warning

An example of suppressing warnings :

public class Bar {
    @SuppressWarnings("deprecation")
    public void m() {
        final var sample = new Sample();
        System.out.println(sample);
    }
}

//> javac -Xlint:deprecation Bar.java
// <No errors and warnings>

An example of a warning :

@Deprecated(forRemoval = true)
public class Sample {
}

public class Foo {
    public void m() {
        final var sample = new Sample();
        System.out.println(sample);
    }
}

//> javac Foo.java
//Foo.java:5: warning: [removal] Sample in unnamed package has been deprecated and marked for removal
//        final var sample = new Sample();
//                               ^
//1 warning

An example of suppressing warnings :

public class Bar {
    @SuppressWarnings("removal")
    public void m() {
        final var sample = new Sample();
        System.out.println(sample);
    }
}

//> javac Bar.java
// <No errors and warnings>

An example of a warning :

public class Foo {
    public void m() {
        final var t = Thread.ofVirtual();
        System.out.println(t);
    }
}

//> javac --enable-preview --release 20 -Xlint:preview Foo.java
//Foo.java:5: warning: [preview] ofVirtual() is a preview API and may be removed in a future release.
//        final var t = Thread.ofVirtual();
//                            ^
//1 warning

An example of suppressing warnings :

public class Bar {
    @SuppressWarnings("preview")
    public void m() {
        final var t = Thread.ofVirtual();
        System.out.println(t);
    }
}

//> javac --enable-preview --release 20 -Xlint:preview Bar.java
// <No errors and warnings>

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