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copied!<p>I do not think you can enforce this at compile time. Please look at the workaround which ensures this at run time.</p> <pre><code>class Tester { public static void main(String[] args) { SnowLion lion = new SnowLion(); // This will throw IllegalArgumentException Bear bear = new Bear(); } } abstract class Animal<T extends Animal<T>> { protected Animal(Class<T> implClazz) { if (!implClazz.isAssignableFrom(getClass())) { throw new IllegalArgumentException(); } } abstract void partner(T other); } class Lion extends Animal<Lion> { public Lion() { super(Lion.class); } int areaUnderControl; @Override public void partner(Lion other) { this.areaUnderControl += other.areaUnderControl; } } class Human extends Animal<Human> { public Human() { super(Human.class); } int money; @Override public void partner(Human other) { this.money += other.money; } } class Bear extends Animal<Lion> { public Bear() { super(Lion.class); } int honey; @Override public void partner(Lion other) { this.honey += other.areaUnderControl; // Problem } } class SnowLion extends Lion { int snowAreaUnderControl; public SnowLion() { super(); } @Override public void partner(Lion other) { this.snowAreaUnderControl += other.areaUnderControl; } } </code></pre> <p>I got this idea from <a href="https://stackoverflow.com/questions/1627581/java-generics-to-enforce-return-type-of-abstract-method/1627633#1627633">Java generics to enforce return type of abstract method</a></p> <p>Hope this helps. </p>

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