@Shadow

@Shadow is used as placeholders for in a Mixin class. Where you would want to access fields and methods like how you would if you were working in the class you are Mixin'ing.

Arguments

remap

[Optional Boolean, default value: true]

The annotation processor will skip this if this is false. With the refmap skipping over this member. This is useful for members originating from mods and not Vanilla Minecraft.

aliases

[Optional String Array, default value: {}]

This can be populated with other aliases, particularly useful when shadowing synthetic members, or if the member is known to have name-changes at runtime from other sources of transformation

prefix

[Optional String, default value: "shadow$"]

For compilers it is illegal to allow methods to have the same name, same arguments, regardless of the return types. This may be an issue when using @Shadow. Hence the prefix takes care of that for you, at runtime when the mixin is being applied, the name will be restored with the prefix removed.

public class Illegal {

    protected String method(String argument) {
        return "";
    }

    protected int method(String argument) {
        return 0;
    }

}

public class Legal {

    @Shadow(prefix = "alt$")
    protected String alt$method(String argument) {
        return "";
    }

    protected int method(String argument) {
        return 0;
    }

}

Usages

Shadowing a Field

Target.java

public class Target {

    private String privateValue = "Hello World";
    protected int protectedValue = 42;

}

Example.java

@Mixin(Target.class)
public class Example {

    @Shadow private String privateValue = null; // Will not affect original field

    @Shadow protected int protectedValue = 0; // Will not affect original field

}

Shadowing a Method

Target.java

public class Target {

    public void method() {
        // ...
    }

    public int fruitfulMethod() {
        // ...
    }

}

Example.java

@Mixin(Target.class)
public class Example {

    @Shadow public void method() { }

    // If the method needs to return something
    // You can return primitive defaults or null
    // But throwing an exception here helps if something goes extremely wrong
    @Shadow public int fruitfulMethod() {
        throw new AssertionError(); 
    }

}