Getter和@Nonnull [英] Getter and @Nonnull

问题描述

我从Eclipse的一个警告，我知道我可以用燮preSS警告删除，但我想preFER明白是什么使得它的东西它可能为空。

I get a warning from eclipse and I know I can remove it with suppress warning but I'd prefer to understand what makes it thing it could be null.

package-info.java

package-info.java

@ParametersAreNonnullByDefault
package test;

import javax.annotation.ParametersAreNonnullByDefault;

test.java

test.java

package test;


public class Test {
    public static void main( final String[ ] args ) {
        System.out.println( new Test( "a" ).getS( ) );
    }

    private final String s;

    public Test( final String s ) {
        this.s = s;
    }

    public String getS( ) {
        return this.s;//Null type safety: The expression of type String needs unchecked conversion to conform to '@Nonnull String'
    }
}

我不明白为什么我得到这样的警告...

I don't get why I get this warning...

PS：

公开测试（@Nonnull最后一个String）{ - >的NULL的含量注释是多余的适用于该位置的默认

public Test( @Nonnull final String s ) { -> The nullness annotation is redundant with a default that applies to this location

@Nonnull私人最终的String; - >没有什么变化

@Nonnull private final String s; -> nothing changes

推荐答案

的问题是，@Nonnull标注有场无影响。它仅支持：

The problem is that the @Nonnull annotation has no effects on fields. It is only supported for:

• 方法参数


• 方法的返回值


• 局部变量（一个code座内）

<一个href=\"http://help.eclipse.org/juno/index.jsp?topic=/org.eclipse.jdt.doc.user/tasks/task-using_null_annotations.htm\">See Eclipse文档

所以很明显 - 作为非空不上的字段检查 - 编译器不知道Test.s为非空和抱怨它。

明显的解决方案确实是在球场上获得加@燮pressWarnings（空）（或方法，如果它是一个简单的getter）：

So quite obviously - as Nonnull is not checked on fields - the compiler doesn't know that Test.s is Nonnull and complains about it.

The obvious solution would indeed be to add a @SuppressWarnings("null") on the field access (or on the method, if it's a simple getter):

public String getS() {
    @SuppressWarnings("null")
    @Nonnull String s = this.s;
    return s;
}

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