When do you use bounded type parameters in Java?

Uses bounds to express capabilities required by generic code and distinguishes them from wildcard flexibility at call sites.

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A bounded type parameter restricts which types may be substituted and lets generic code use the bound's operations. For example, <T extends Comparable<? super T>> T max(List<T> values) says every element can be compared in a compatible way and the result has the same type as the elements. An upper bound uses extends for classes and interfaces. Multiple bounds are allowed, with at most one class bound and that class listed first.

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Generic method design, upper bounds, multiple bounds, type relationships, and restraint in public signatures.

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A bound is valuable when the generic implementation needs operations that plain Object does not provide.
A bounded type parameter restricts which types may be substituted and lets generic code use the bound's operations. For example, <T extends Comparable<? super T>> T max(List<T> values) says every element can be compared in a compatible way and the result has the same type as the elements. An upper bound uses extends for classes and interfaces. Multiple bounds are allowed, with at most one class bound and that class listed first.
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A named type parameter is especially useful when the same type relationship appears in several parameters or in the return value. If a method only needs to read values through one common supertype, a wildcard may be simpler. Bounds should describe a real capability, such as comparison or a domain protocol, rather than requiring a large implementation class merely because it is convenient. Narrow interfaces keep the generic method reusable.

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Adding a bound when the implementation never uses it.
Using a concrete implementation class as an unnecessarily broad capability.
Forgetting that a type parameter can relate inputs to a return value.
Exposing complex bounds everywhere instead of containing them.

When do you use bounded type parameters in Java?

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