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The return statement is a branching control flow instruction that immediately terminates the execution of the current method, constructor, or lambda expression, and transfers control back to the invocation point. It is strictly responsible for satisfying the declared return type of the executing block by evaluating and passing back a compatible value, or simply halting execution in void methods and constructors.

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Syntax

return [expression];

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Execution Mechanics and Compiler Rules

Type Compatibility If a method or lambda signature specifies a non-void return type, the return statement must include an expression. The evaluated type of this expression must be assignment-compatible with the declared return type. The Java compiler permits exact type matches, implicit primitive widening conversions, autoboxing/unboxing, and reference type upcasting (polymorphism). 
public long getIdentifier() {
    int id = 1024;
    return id; // Valid: Implicit widening conversion from int to long
}
Void Methods and Constructors Methods declared with the void keyword and class constructors do not yield a value. In these contexts, the return statement is optional. If used, it must appear without an expression (return;) and serves solely to force an immediate exit from the method or constructor’s execution stack. 
public class Processor {
    public Processor() {
        return; // Valid: Halts constructor execution without returning a value
    }
}
Lambda Expressions When executed inside a block lambda expression, a return statement only terminates the execution of the lambda body itself, not the enclosing method that defines or invokes the lambda. The return expression must satisfy the return type of the target functional interface. 
Function<Integer, String> formatter = (num) -> {
    return "Number: " + num; // Terminates the lambda, not the enclosing method
};
Unreachable Code Because the return statement unconditionally transfers control out of the current execution block, any statements written sequentially after a return within the same lexical scope cannot be executed. The Java compiler performs static flow analysis and will flag this as an Unreachable code compilation error. 
public int compute() {
    return 42;
    int x = 10; // Compile-time error: Unreachable code
}
Interaction with finally Blocks When a return statement is encountered inside a try or catch block, the JVM evaluates the return expression (if any) but suspends the actual return operation. Control is temporarily routed to the finally block. If the finally block completes normally, the suspended return operation resumes, passing the originally evaluated value to the caller. However, if the finally block contains its own return statement, it abruptly terminates the block and permanently overrides the initial return value. 
public int getStatus() {
    try {
        return 1; // Evaluated, but execution is suspended
    } finally {
        return 2; // Overrides the previous return; method yields 2
    }
}
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