Lazy vs Eager Evaluation

Evaluation strategy determines when expressions are executed.

In Java (especially Streams), understanding lazy vs eager evaluation is essential for writing efficient and predictable code.

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Basic Difference

Lazy Evaluation	Eager Evaluation
Executes only when needed	Executes immediately
Delays computation	Computes right away
Improves performance	May waste computation
Used in Streams (intermediate ops)	Used in Collections & normal method calls

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What is Eager Evaluation?

Eager evaluation means:

Expression is evaluated immediately when it is encountered.

Example (Normal Java Method Call)

public static String getValue() {
    System.out.println("Executed");
    return "Hello";
}

String value = getValue();

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What is Lazy Evaluation?

Lazy evaluation means:

Computation is delayed until the result is actually needed.

In Streams:

• Intermediate operations are lazy
• Execution starts only at terminal operation

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Lazy evaluation delays execution until a terminal operation is invoked.
In Java Streams, intermediate operations like map() and filter() are lazy, while terminal operations like collect() and forEach() trigger execution.
Eager evaluation, on the other hand, executes immediately.