X.java

import java.io.InputStream;

public class X {
    public static void main(String[] args) {
        new X().write(null);
        //     ^
        // X.java:5: reference to write is ambiguous, both method write(java.lang.String) in X and method write(java.io.InputStream) in X match
    }

    public void write(Object o) {
        System.out.println("Object");
    }

    public void write(String o) {
        System.out.println("String");
    }

    public void write(InputStream o) {
        System.out.println("InputStream");
    }
}

Y.java

public class Y {
    public static void main(String[] args) {
        new Y().write(null);
        // => "String"
    }

    public void write(Object o) {
        System.out.println("Object");
    }

    public void write(String o) {
        System.out.println("String");
    }
}